NPCs and Captured Gear

A group of hero PCs have been captured, and their gear stripped from them. Their captors (pirates, bandits, or some other villains primarily interested in loot) are actively using the captured weapons, armor, and consumables when the PCs attempt a violent escape.

How is one expected to run the resulting encounter(s) in 2nd Edition? Are the captors' stat blocks altered by any of the permanent gear? Can they make ready use of the consumables? Should their effective level be adjusted to account for any such changes?

What other issues might a GM need navigate in such a scenario?

I don't think anyone cares about the actual stats of the captors. What players want is to feel that the captors have captured their gear. So give one piece of equipment to each captor and build them around this piece of equipment so the player having lost the equipment will really hate being pounded by the very same sword they're used to wield.

For example, the captor who took the sword should be an offensively oriented character. The one who took the Paladin's armor should be an AC tank. The one who took the Wizard Staff should make a massive use of the spells in it. Etc...

Depends on the level of the gear. We can use the weak and elite templates as a reference point, which basically amounts to a +/-2 adjustment being equal to one level. But the big difference is in damage. Losing runes means the PCs only hit slightly less often but significantly less hard and martials will take much longer to wear down enemy health.

Ways around this include ABP or dropping a striking weapon or two early on, perhaps on the guards of their cell.

The other big variable is armor type. The heavier the armor, the lower your PCs dexterity will likely be, and the bigger their shift in vulnerability will be. A monk just loses their potency runes, max +3, but a paladin loses their full plate, which is max +9.

Give a temporary Barbarian MC Dedication to the PCs when they realize what is happening, with free bonus to hit when the bad guys use the consumables.

BTW increase the loot of the encounter with the cost of the used consumables.

Best for the PCs to take down their now enhanced opponents one by one. They should make their captors split the party.

I don't think "expected" is a good word to include in the question because there really isn't an expectation of any kind that this sort of scenario happen on a regular basis (or at all).

So instead I'll answer how I think this could be run without the players feeling overly disadvantaged:

Step one for that is to not have both the NPCs get the bonuses from the PCs' gear and the PCs be facing encounters un-geared. So either use the "they've got your gear" as a flavor detail that barely (if at all) modifies the enemy stats, or have the PCs face the encounters with useful gear that just happens to not be their own (such as what their captors would have been using prior to capturing the PCs).

Step two is to make sure there are numerous avenues to deal with recovery that aren't just possible, but are actually relatively equally viable. For example, being able to isolate and overwhelm a small number of foes (even just 1), or utilize environmental elements to take down a foe and recover some gear (something as simple as being able to improvise a trap to lure someone into), or even a way for the party to say "let's just get out of here" and go get some kind of help to come back later and recover their belongings.

Enemy stats already assume the players are using available magic weapons and armor. Given that, outside of property runes perhaps, the items themselves should do nothing to alter the enemy since the PCs effectively have a debuff to attack, damage, AC and saves until they get their equipment back. Heavy armor characters especially will have their AC crater and be crit to death in the first encounter.

Essentially, the math requirements of pf2e don't really support this kind of encounter outside of the very earliest levels or ABP.

I think that this has been said already, but I will concur - the enemy having the PC equipment shouldn't change the stats of the enemy as far as HP, AC, attack bonus, or damage. It might change the damage types. It might mean creating custom enemies that would be expected to use that type of equipment.

The bigger problem is going to be having the players being able to battle effectively while missing most or all of their equipment. Some classes and builds are going to be more disadvantaged by that than others. Maybe that is a good thing - maybe it isn't.

As for it being a good thing, it can be kinda cool to see how the standard party combat roles change because of the lack of equipment. A spellcaster may end up layering on defensive spells and taking more of a front-line role than the +0 DEX Champion can handle when missing their armor. It can make for an interesting one-off combat.

If you are planning in this sort of thing in advance the best way to set it up is for them to be captured by an Extreme+ amount of lower level foes. This way you can keep verisimilitude by having the gear give a noticeable power up (spread out across many foes) without it being overpowering, and the enemy save DCs are low enough that PCs can successfully engage in disarm, restraints etc.

Also remember to include some of the downsides of the gear. The ruffian who dons your fighter plate armour can be made comically slow as they don't have the strength. The bandit e
Rogue might see a base damage increase but they no longer have the traits to do sneak damage etc.

The other option is to have them be in the process of stripping runes of things, to avoid the aforementioned downsides, or because the local fences prefer to flog runestones over probably quite recognizable swords and armour.

I think you should change their stats, yet that also means changing their levels and how you distribute them in encounters. It also might make them arrogant, divisive, and however else flawed you need them to achieve encounter balance and narrative interest. Heck, maybe there was a Tolkien-inspired bloodbath fighting over such nice items. Or maybe some fled w/ items the PCs will want to track down (if only for personal justice), thus hooking the PCs into the next adventure or scenario.
It's a fairly unique opportunity, so exploit the narrative options available, including perhaps a portion where they have to Skill their way past some obstacles they'd usually combat through. A simple prison break and overpowering of the guards would waste these chances IMO.

Oh, and if this is just a prospective adventure, capturing PCs takes finesse. Usually it's better to capture them through narration because players will be quick to spot a situation that robs them of agency; there's no reason (to pretend) to play that out if it's required for your campaign. If it does just happen, then that's cool, and you might be able to find just the right difficulty and pressure which does this, but given how many resources PCs have ("Aha, I pull my scroll of Dim Door!") this can be difficult without again, players spotting the obviousness of it.

Oh yeah actually pulling off a PC capture is a whole topic on its own. This is assuming you did it in a way that doesn't make campaign blow up;

Enemies have stats appropriate to their level. If you increase their power by giving them better gear on top of that, they're now effectively higher level. Don't try to fool yourself here. Either accept that "yes, these are now effectively a level stronger" or so; or don't bump up their stats, just bend them so that you can say "they used to be weaker but thanks to YOUR GEAR they're now this level (which you were aiming for all along)".

Meanwhile, the PCs are effectively lower level thanks to not having their gear. How much lower level? That depends, the gap gets bigger at higher level. Someone who normally has a +2 to hit 3d10 sword and now only has his 1d4 fists? That's a BIG difference. As an extremely crude rule of thumb, I'd rate the PCs at least one level lower, plus one more level lower for each tier of Striking rune they're down. And that might be underestimating it. So a level 5 party without their gear would be more like a level 3 party; what used to be a moderate encounter for a level 5 party is more like extreme now.

Meanwhile, the PCs are effectively lower level thanks to not having their gear. How much lower level? That depends, the gap gets bigger at higher level. Someone who normally has a +2 to hit 3d10 sword and now only has his 1d4 fists? That's a BIG difference. As an extremely crude rule of thumb, I'd rate the PCs at least one level lower, plus one more level lower for each tier of Striking rune they're down. And that might be underestimating it. So a level 5 party without their gear would be more like a level 3 party; what used to be a moderate encounter for a level 5 party is more like extreme now.

I once ran a battle where the PCs lacked their gear. In Forest of Spirits I declared that the city of Ordu-Aganhei did not let townsfolk carry weapons. I made an exception for the fighter Jao because his player loved to deal massive damage. Since Jao was the declared owner of a caravan, he counted as minor nobility and could carry one weapon, his greatsword, to show his status.

Then while traveling the streets with the local prince, enemy ninjas attacked the party. The guards rallied around the prince, leaving the party to defend themselves. The fighter had his greatsword. The samurai grabbed a tent pole off of a nearby booth as an improvised weapon. The ninja had weapons hidden on herself. The spellcasters had their spells. The rest took weapons off of fallen enemy ninjas. Re-arming was pretty quick.

This was under PF1 rules, so the weapons had nothing as impressive as a Greater Striking Rune. But the party was under-equipped for their level anyway, because the players did not care for updating gear.

Assume that the party will soon have the average gear of their enemies. And since those enemies captured the party, their gear won't be awful.

It may be worth making sure there are viable non-combat ways for the party to capture or incapacitate their captors. That way, you can make the captors themselves overpowered relative to the PCs (because of the gear), but give the party an avenue of escape, and then allow them the opportunity to use the environment itself as a weapon. Maybe even leave a cache of items they could use against their captors, like scrolls or snares or the like. The guy that stole the Paladin's armour isn't really going to be in good shape if the casters find a few scrolls of heat metal, for instance.