How close is Howler standing to Ulthok? You were slammed about 15 ft away from him.
What does the hall away from the chamber look like, what does Ulthok see if chooses to run? If it is just a straight hall then there is little advantage to running, he is still an open target. If there is a crossing hall he might at least get out of direct line of fire for spells or what-not. To the East, the opposite direction from the chamber, you can barely see what looks like a tiny star of light.
By barreling into Ulthok in leads me to think Howler was more interested in protecting the stone than actually hurting Ulthok. Ulthok has found something important.??
I really wish Ulthok's ring of invisibility was working. That really evens things up for a little guy I don't know have you tried it?
Oh and since Xin put out the fire on Peri how long will she remain out. Does she need some healing to regain consciousness. You don't know you have not been able to check on her since it all happened.
Can Sirene's cat cast Reduce on the one remaining big Hydra? I don't know can it? Try it and see.