The mask Morokei glitched off my companion
Solution 1:
This is a known bug:
If any mask is given to any follower, over time it may disappear from their inventory.
So, as you stated, your options are limited to continuing from an earlier save point, or start over.
The good news is, this is not plot essential; it is only required in order to gain the Konahrik mask, so you can continue on with the game.