In my older playthroughs, trolls generated by the vicinity of a cave (whether inside or outside the cave) did NOT respawn. However, on this current playthrough, it really does seem like the troll cave near my base at the Trader's Camp does have respawning trolls (on the outside).

And of course you can get randomly-generated trolls in any part of the Black FOrest, and (obviously) the ones that spawn through "The Ground is SHaking" raid event.