I joined the Stormcloak Rebellion and of course we conquered the Imperials and Ulfric is in charge. However, I've been wandering a little and just came across the Falkreath Imperial Camp. I set about destroying it and took out all soldiers but was incapable of killing Skulnar. I could bring him to his knees, with a little help from the lovely flame atronachs, but no matter how I hacked at him he'd bounce back. Did it about three times and gave up. Why is he immortal?

Unfortunately, whichever side you pick in the civil war, the other side's generals/captains/whoever is in charge of the camps can't be killed. Someone didn't set the flag to make them killable after the war ends.

If you're on pc, there is a mod that fixes that.

Thanks Tataran. I thought I was going nuts: I ploughed 50 arrows into the guy and then hacked him with my Dawnbreaker but he lives on ... forever. Actually, I was surprised to find an Imperial camp still existing but I suppose they're all over Skyrim.