what ever you do, do NOT cast oil apocalypse.
EDIT:
found a way to use it (not fully sure):
step 1 - use healing mage (not certain its necessary, but if im right he has something that makes it so he is guaranteed to heal.)
step 2 - get wall spell (and heal and oil and apocalypse)
step 3 - surround yourself with healing fire (this also makes you almost invincible, not just in this scenario, but in general.)
step 4 - use oil apocalypse and pray.
step 5 - anytime the healing fire goes out (or a reachable gap is created in the oil fire) use heal wall to make more healing fire.
step 6 - repeat step 5 until every oil fire goes out. (or you die)
survival possible, but not guarantied.
possibly improvable through water spells, but i dont want to test.