So, after playing this game since 2011, I've encountered something that's never happened to me before! On my current 'jack of all trades character' the first quest line I completed was the Companions way back at lowly level 15ish.

Since then I have gone on to to do all the other faction (except CW), main, and dlc quests; and I am now level 54. I've been a werewolf the entire time, and recently decided I was going to cure myself after going back and completing Purity for Farkas or Vilkas.

Lo and behold I return to Jorrvaskr, walk in the front door and Skjor is standing there talking to Aela! Normally I wouldn't mind a dead NPC returning, except that I think it broke the companions quest line, because I can't get purity to start.

Is this a pretty common bug? I play on the 360.

Skjor had a habit of returning from the Hunting Grounds of Hircine on many of My Companion characters before the USKP existed.

Have You done enough random Quests for Vilkas and Farkas? Aela also requires a few random Quests for aquiring the three Totems of Hircine.

If You are lucky Farkas may send You to beat up Nazeem.

I did get the Totem request from Aela but the quest never activated.

As for Vilkas and Farkas, I did a couple more side quests with Vilkas, but Farkas doesn't have the option for more work anymore.

Check the UESP for Bugs with Purity.

Hmm, looks like there's a couple solutions to try out. Probably should have looked there first, but I just thought it was an interesting event.

Skjor comes back because there was an alias in an aftermath random encounter with the Companions wandering about Skyrim that did not correctly omit Companions characters that were dead. As a result, sometimes it chose Skjor, and then would resurrect him. USKP stomped that bug a long while ago. I think it may have even been before Arthmoor took over as the curator.

Ah! So that is why when I do the Companion's Quest I sometimes see Skjor "sliding" about Skyrim in his "dead state."