You can get the staff without the quest line?
That I'm not certain about because I've never obtained it without the quest line. The priest will be in Labyrinthian anyway and he will have the mask (I'm assuming, because the masks are
always there whether you kill them as part of a quest or not).
Have you checked the bug forums? Or tried an earlier save? Or zoned in/out of Mzulft to see if the guy will die like he's supposed to?
I've had glitches happen where I basically had to just wander off and do another quest and then come back to it, and it would work fine. Glitchy game is glitchy.
