Many a beast has seen MY backside and a cloud of dust!
...unless your DM likes puzzles. Solving the issue of a seemingly unkillable troll* is a perfectly valid conundrum.
* you drown it, suffocate it, starve it, petrify it, trap it in stone, use a Wish, use a necromantic "killing" spell, use a Con-destroying poison, find & use the campaign-specific unkillable troll killing weapon, etc.