I am playing through Skyrim on the Xbox 360 and have 49/50 achievements competed. Earlier in the game, to gather a 1000 gold bounty in every city, I went into Dawnstar and slaughtered the first few guards I saw. Without realizing it, my companion killed the leader of the museum.
My last achievement, "Oblivion Walker", was to complete 15 Daedric quests. I completed 14/15, and then saw that I still had "Pieces of the Past". I went to try and start the quest, but was unable to. I searched through Dawnstar, but could not visit the measure any longer.
Do I need to restart my game from a previous save before my companion slaughtered the museum leader? If so, do I need to have all 15 done at the same time, or will I get the achievement upon completion of that quest?