I'd see how it goes, and if the answer is "poorly", then you have a conversation with them. Aside from forcing someone to change classes, toning down the enemies is also an option if no one wants to play something sturdier.
Consider the five assignments that the PCs receive during their first week.
1. Rain-Scribe Assignment: buy rare chickens
2. Tempest-Sun Assignment: Chase gremlins out of a storeroom
3. Cascade Bearers Assignment: Gather ingredients for a ritual
4. Emerald Boughs Assignment: Deliver the mail
5. Uzunjati Assignment: Tell a story about your projects
Only two have combat: the gremlins and gathering ingredients. This module is light on combat and mostly awards experience points for finished projects. The players have a chance to level up without much danger.
For the gremlins, I had Esi Djana emphasize to the party that the gremlins on campus are tame. If the party deals only nonlethal damage to them, then the gremlins will respond with nonlethal damage. Thus, the players would be merely knocked out if the gremlins won. However. this was a problem for the spellcasters, because most spells deal lethal damage. But Esi arranged for supply manager Xhokan to lend them nonlethal weapons. And the ghoran bard Stargazer also equipped herself with gremlin bells and managed an Intimidation check to scare a gremlin into running away.
The gathering ingredients assignment was actually dangerous, due to the myceloid Umbo. He infected on PC with purple pox, so I had to add a health clinic to the Magaambya to cure it. But it is only a Moderate-Threat encounter, so fatalities are unlikely. And the PCs will need some real practice to learn how to fight as a team.
In general, I have been trying to have the Magaambya protect the students. If a teacher is involved, they will be exposed to only Trivial Threats. They fought a 6th-level Will-o'-Wisp on a class trip, but I gave them so much forewarning and help that the battle was Trivial Threat.
However, they run into unexpected threats, such as Umbo and the attack on the Introduction Ceremony that can be seriously dangerous. For the attack at the Introduction Ceremony, I had a passing student run to fetch the teachers, who showed up just as the party finished the battle. Teachers are an emergency rescue if needed.
Now my party is 3rd level in Section C, The Infested Caverns. Those non-dangerous fights taught them how to work together, so they are handling the dangerous fights in the caverns just fine. Except for the Wasp Swarm I added. That was nasty, and the party had trouble curing the venom on the magus. Don't add a Wasp Swarm.
I'm worried with this party combination player deaths are very likely as they're in the middle of the first big dungeon in the AP, and thinking about my options. Should I have a conversation with my players to bring this up with them, and suggest at least one of them rebuilds their character to be a martial character? Or should I just see how things play out and give them an option to build a new character or rebuild their character in the case of a player death?
Oops, "the first big dungeon in the AP" is the Infested Caverns, isn't it. I did not notice when writing my previous post that you are that far along.
My party is short on healing, so I made up a 4th-level conversant character, Orrick Majivu, to be the leader of their tunnel-clearing group. Even though the teachers thought that the tunnels under the Archhorn Library were relatively safe, they were not going to send a group of initiates without protective supervision.
Orrick Majivu Creature 4
UNIQUE NG MEDIUM HUMAN HUMANOID
Male human sorcerer with phoenix bloodline
Branch Rain-Guides conversant
Perception +8
Languages Common, Chelish, Mwangi, Osiriani
Skills Arcana +10, Athletics +6, Crafting +8, Diplomacy +9, Intimidation +9, Medicine +10, Nature +8, Society+8 , Warfare Lore +8
Str +0, Dex +1, Con +1, Int +2, Wis +2, Cha +3
Items explorer's clothing, +1 striking staff, 2 scrolls of 1st-level heal, healer's tools
Battle Medicine
Diehard
Magical Crafting
Unusual Treatment
Wizard Dedication (School of Battle Magic)
Arcane School Spell (Force Bolt)
AC 17; Fort +7, Ref +7, Will +10
HP 36
Speed 25 feet
Melee [one-action] +1 striking staff (Two-Hand 1d8) Damage 2d4 bludgeoning
Primal Spontaneous Spells DC 19, attack +9
2nd (4/day) blazing bolt, clear mind, see the unseen, sound body
1st (4/day) breathe fire, cleanse cuisine, heal (signature), fleet step, XX(Heal)
Cantrips (2nd) detact magic, electric arc, light, needle darts, prestidigitation
Bloodline Spells, 2 Focus Points, rejuvenating flames,
Arcane Prepared Spells DC 18, attack +22;
Cantrips (1st) telekinetic hand, message
Wizard School Spells DC 30, 2 Focus Points; force bolt
Orrick works in the health clinic and is good at tending to student injuries. But he relies on the more worldly PCs to invent combat tactics.
But if they are already in the middle of the Infested Caverns, the events are too far along to give them a protector.
By the way, a bard and a magus are semi-martial classes. Some builds reduce the martial aspect, but can't those two in your party protect the druid and wizard? Also remember that the PCs can retreat back to Archhorn Library for a safe rest to Treat Wounds and Refocus.
Yesterday, the party in my Strength of Thousands game finished the Infested Caverns in Kindled Magic. The combat did not follow any expectations, due to a pair of critical successes.
The party had cleared the rest of the Infested Caverns when they entered the final Nest Room C7d, in which I placed three vexgit gremlins, creature 1. The party was already 4th level (I let them level up in mid-dungeon), so this was a Trivial-Threat battle. The party gave themselves the extra challenge of capturing all the gremlins alive and unconscious, and they did that here, but they delayed on hauling the unconscious vexgits to the Staging Room C1 for their safety. Instead, the 8 characters lined up to the secret door to the Stone Ghost's Room C15 and opened the door.
The Stone Ghost rolled highest on initiative. Three members of the party had disguised themselves using the masks and cloaks from the Gruesome Trophy Room C14, which led the Stone Ghost to assume that the party had a plan. And 8 students would have been a challenge to fight, even if they were as weak as 1st level. He walked through the wall out of the room to find some gremlins and giant insects to give himself a greater advantage.
The Stone Ghost was gone for a while (he was discovering that the party had defeated all his nearby forces). The party had time to intimidate and interrogate the jinkin gremlins (one PC spoke Undercommon/Savroth), find and read the Stone Ghost's notes, and decide to loot his easy chair and bathtub. They had an excuse for the bathtub: they put unconscious vexgits into it for easier transportation.
The Stone Ghost ambushed them in the Centipede Trap Room C4 (the party had already disabled the traps). He Strode over to the bard Jinx Fuun and used his Entombing Grasp on her, proclaiming that he would not let them escape after they had destroyed his minions. And he rolled a critical success, entombing Jinx underground completely. The player calculated that she had six rounds before suffocation.
This also left the Stone Ghost exposed, since he had no actions left to retreat into the wall again.
The other bard already had Inspire Courage/Courageous Anthem going, just in case (Jinx Fuun had been singing Triple Time foe extra speed). The champion Wilfred strode up to the Stone Ghost and stabbed him with his +1 striking Blade Ally longsword. Blade Ally says, "For a champion following the tenets of good, choose disrupting, ghost touch, returning, or shifting." Since past encounters with the gremlins had given them the name "Stone Ghost," Wilfred had chosen ghost touch.
Boosted by the Courageous Anthem, Wilfred managed a critical hit. He rolled 2d8+4(str)+1(courageous anthem), got 7 and 8 on the dice, and doubled it for 40 damage. The Stone Ghost has only 40 hit points. He was down in one blow, due to the party's preparation and teamwork.
Thus, one martial characer is enough to defeat the Stone Ghost, if the dice love him.
And the wizard Idris had Force Barrage prepared, so he could have finished off the Stone Ghost if Wilfred rolled less damage.
Next the PCs had to hurriedly dig Jinx Fuun out of the dirt before she suffocated. That required two rounds.
The players were satisfied with this unusually short combat, because of the drama of the two critical successes. The Stone Ghost had demonstrated how deadly he could be, and in response Wilfred had demonstrated that he could be just as deadly.
The Stone Ghost actually stabilized, so the fast elf magus ran back to the surface to fetch teachers. Wilfred kept the Stone Ghost unconscious with regular nonlethal strikes from his ghost-touch longsword while the party waited for the teachers.
The teachers locked the Stone Ghost AKA expelled student Uduak Basni into a force cage and woke him up for a trial. Presented with the gruesome trophies as evidence of murder, the Stone Ghost bragged of his crimes and was found guilty. The teachers executed him before the force cage expired.