Considering the number of high level spellcasters bumming around Faerun, I feel like it shouldn't be that hard for a sufficiently wealthy character to fix the one Volo mutilated. Wait time for an appointment would be the biggest issue, since there are surely more rich people trying to hire advanced clerics than they have spell slots. If your character survives the game, I think you can assume they get it fixed eventually.

The hag-eye is probably hag-eyed forever, barring wishes. I assume all the less extreme methods of fixing it would result in the replacement becoming hag-eyed as well.