On my oldest character, I've done this quest a long while ago (maybe back in 2011). Today, I loaded up the character, only to see that both Sailor's Repose and the journal entry for the quest are missing. The lighthouse and the abyss, however, were still marked as "Cleared", and I even had Mani's cellar key still in my inventory. I went back, killed all chaurus again, got Habd's remains, put them into the fire, got Sailor's Repose, but still no journal entry or, well, anything. Is it some known issue? Because while I fixed that one, I'm not sure if there were any other quests that I've completed that also disappeared. Could it have something to do with the add-ons, or deleting save files?
People have reported quests disappearing mostly completed ones but rarely ongoing ones. I seem to remember that The Fallen vanished from someones journal before they finished after they left it for a long time. It does usually seems to time that does it, maybe the journal cleans itself after a while or a after a certain amount of quests build up but i don't really know for sure (i very rarely go back and look at finished quest though so never noticed myself).
I wouldn't have noticed it if Sailor's Repose hadn't disappeared along with it. I don't mind the journal cleaning itself up (if that's really the case), it's the active effect's vanishing that worries me.