Immediately after accepting the quest in Riften from Svana to steal Marks of Dibella from her bosses lovers the stable boy got ganked by a dragon and the quest disappeared. Has anyone had this happen and is there an alternate way to fix this? I tried to just kill Haelga while she slept but Svana was just mourning the loss and told me to go away.

Well, hasn't happened to my toons - but normally when this sort of glitch happens in the TES games, I just reload a save prior to the stuffed-up situation.