Its been 8 months since skyrim has been out and still they have not fixed this. I can not get this achievement because the pieces of the pat guy was killed by a dragon. In this game you can not kill Imperial armies leaders at there camps after you have completed the civil war quest line. But probably one of the most important characters in the could be killed by a mud carb ( not likely but still possible) and now because of this I can not get this achievement due to the fact Bethesda decided to make imortal charcters, but aparently not a main character that is need to finish the game.

NPC's die, thats a fact of life in Bethesda games. The MQ and CW questlines are considered "major" questlines so those NPC's in that are marked essential so that they can be completed. The other quests for things like items from the daedre are not considered major quests, so some NPC's are not essential in those.

Basically you need to start a new character to earn the achievement. If your that much of a cheevo hunter your almost certainly used to restarting other games to earn the cheevo's. Sure its a bit svcky but there ya go, thats just the way it is im afraid.

Best of luck in the search.

Here's my slightly different advice, based on what I recently did. First, it requires you save like a fiend. Many of us have dozens, hundreds of saves. This is my second play through so I wanted to try the Stormcloaks quest line. I had already completed the main quest, just waiting for Dawnguard. I reloaded a save before I played Seasons Unending, played through the Civil War, got my achievements, then abandoned that timeline & returned to a later save. I think Ulfric is a d*ck, & I don't want him as high king. Return to earlier saves to complete certain achievements, then go back to your preferred time line without the tediousness of starting from scratch.