How much of the area did the defeat? The cultist have a potion of cure light wounds each in area. They are quite easy to defeat if if you are capable to some decent damage. Easy to hit and low hit point. As long as your two remaining players aren't too low in AC this could get the 2 potion of cure light wounds.
If they really low on HPs have a Mongrelman from the other camp show up to help out. Have Lann show up to help out.
Also don't forget that Aaravashnial has two potions of cure light wounds as well and can cast some spells. Heroism and Magic Circle against Evil. So +2 AV and +2 to hit with a +4 to saves. Add then have him summon a few monsters to help out during the fight. Hostilla shouldn't last long against that even if your 2 remaining you players only have couple hp left.
Once the rescue is done conveniently change the ring of climbing to a scroll of raise dead in the hidden chamber. The scroll can be used by the inquisitor and it's worth 1125 gp, the ring at 1/2 is worth 1250 so a fair trade and gets you party back together.