Get that nasty hacked up molding ridiculousness off of that mirror. And either gut the whole bath to the studs and start over. Or, do nothing, other than actual proper job on mirror replacement, and put in a real ceiling instead of that other hack. The hack work is really bringing it down. The #1 rule if design is to First Do No Harm. You've repeatedly violated that. And that is what needs to be removed and corrected.

how would you put in a ceiling with no clearance, which will mean lowering an already low ceiling? Im all for mirror replacement but taking that down will bring down the drywall with it, which'll bring me back to the original problem of either gutting the whole thing or finding a solution to hanging drywall next to already tiled wall

Just hire a real contractor. You're obviously out of your depth here with the DIY approach. Your assumptions are incorrect. And your hackery is worse.

M(r)s Wheeler. Im sorry if im not on your level, but im quite sure you didnt begin your 40 years in the trenches at the level youre at now. Im up for framing a ceiling if it didnt require either moving the ac ducts that run thru the bathroom or dropping the ceiling anymore than it is. Its less than 8ft. I appreciate the tough talk but id like solution(s) to go along with it.

Ductwork can convert from round to rectangular. It's far easier to reroute than you think. So is patching drywall. You are making mountains out of molehills that a good contractor could solve in about 3 days.

Taking down a glued on mirror will damage the drywall but not destroy it. Wouldn't matter anyway. Easy fix for a pro.

You may be able to just remove the trim, though, and get a bigger vanity. There is no way to remove SOME of the tile.

I really doubt that drywall on the ceiling will require dropping it.

Get a pro.