If you're having trouble keeping your allies around, one thing any PC can do to revive an ally, even without any skills, is to lock them in a stationary restraint, then unlock them. Swap them repeatedly until they're on the tile of the sarcophagus or the mummy's post, then interact to lock them up, then bump them and choose to pick their restraints. They'll be back to 5 HP, and able to follow you back to the Summit.
Bear in mind that they won't otherwise heal after doing this, so it's not an amazing free heal, and is instead only a stupid trick to 'friendly capture' an ally so they can be transported to the Summit, but that'll still get you some extra Servants that you might've otherwise abandoned to their fate.