durig the quest world-eater's eyrie when you have to release Odahviing, Serana went to the release chain and pulled it, she set him free whilst I was still talking to him.

i know she interacts with lots of things but this was unexpected.
I thought it was good that she was able to do this.

Was he like "F**k dis sh*t, I'm out!" or did he stay?

seems the latter, daedric

That would be one messed up glitch if he just flew away.