Yes, if the dominate spell succeeds Festral is able to make them jump.
A ..chaotic hero comes back if the rest of heroes kill him and then resurrect him with an elixir of life (if available)
OR
when heroes destroy the chaos source by droping the ring into the pit. Everyone could guess that Festral is wearing it. So the rest party focuses on Festral. If they kill him and discover that he was not wearing it, they have to continue searching (with a chaotic-Barbarian or Dwarf hitting them all the time
, a sleep spell maybe could help here) until the ring is found and then break the spell.
Serious disadvantage: heroes until this quest don't know the effects of dominate spell, it appears here for 1st time
(it's up to morcar to introduce it at the begining of the quest pack).
Also "tempest" spell proves for once again (in my opinion ofc) that it's the top air spell. I think 2 rounds are enough for an experienced party to kill Festral (3b.p) without saying "dom..