Is it a window well on the moisture wall?
I thought the bathroom was all block
Please stop basement shaming me. Some of us can't have basements!
Fixing it from the outside is exactly what I'd do and I'd try to set it up so I wouldn't cover it inside until confident it's fixed. It also seems pretty separate so no push to get it done?
Bathroom wall opening up is great, that's some heavy duty looking plaster. Are you going to try to redo drains? Uber will get upset over that s trap, with the wall open you may be able to at least put in an aav somewhere.