Only if this is scripted as a part of a quest or something that makes sense like Caninelegion mentions.
But as a general rule I prefer when there is not respawning monsters because it will not have the same quality of the tailored encounters made by Larian level designers (or whatever is the title of the persons making the encounters at Larian).

If you want respawning monster to have unlimited loots and/or xp it's better to have some kind of arena or a constrained feature instead of having a generic respawn everywhere.