So, early on with my current character I cleared out a tower full of bandits. The name of the place was Nilheim. About ten hours later I got a quest saying I needed to kill the bandit leader who lived there. I returned, but the place is cleared with all the bodies still scattered about the place. I searched UESP to see if I could discover anything only to find that there is a different miscellaneous quest associated with the place. The quest I have in my journal is not the same, and from all appearances is a radiant quest. I'm thinking to go looking for Telrav (the misc quest giver) to see if it will fix it.

I've read more than once that some radiant quests malfunction. How often would you say that happens? How do you fix it?

Only radiant quests I've had consistent problem with are giant and dragon bounties, in which you get a bounty to clear out a dragon altar or giant camp but it's already been cleared, so the quest just stays in your inventory. They're supposed to respawn but it either takes a very long time or that issue is also broken. The cell reset for most dungeons/etc. that are cleared is either 10 days or 30 days, so if you want to wait that long and see if it clears out, that's an option. Still, I usually end up using the console to advance the quest since I'm OCD about my quest log.

If you stay away from that tower for several game-days (I have seen anywhere from three to ten mentioned) it should respawn all the bad guys and loot.
But you must stay away, rather than checking back every day to see if it's ready yet. If you are REALLY determined, you could fast travel back-and-forth
between the College and Markarth (21 hours each way) six times or so.