My question: After completing a task, do you have to re-roll the dice or is it ok to fail the adventure right after that?

It happened in a game yesterday. So a monster was holding my yellow dice and it was on an adventure where it was impossible to clear (it needs 8 dice so I need to unlock the yellow dice first) So I decided to just kill the monster to get my dice back and quickly fail the adventure. The problem was, there was a terror effect on the adventure card and I don't want to roll an impossible adventure just to get the terror effect.

Thanks

shattering said:

Well, the rules tell us…

Regardless of whether or not the active player resolved any
Terror effects, he must then do one of the following:

1. Attempt again to complete a task.
2. Fail to resolve the Adventure card.

This seems to suggest you have a choice, i.e. you can decide to make another attempt or you decide that you have failed.

So I would say in your case you can decide to fail the Adventure if you so wish.