Today's your day haha - there is actually a Bitsy hack for basic savegame functions:
https://github.com/seleb/bitsy-hacks/blob/main/dist/save.js
I haven't tried it myself yet but implementation seems easy. There could be compatibility issues with other hacks though.
Btw I just released my first ever Bitsy game today and it would mean a lot if you would check it out. (You can play it here on itch via my profile) It's made with Bitsy 3D and while I was playing your game I was thinking how cool it would be to have Metrodungeon extended and in a 3D environment... so if you ever have too much time and you like my style - I would be really interested in a collab since i honestly think this game is one of the best Bitsy games I played.
I love your game! Bitsy in 3D works really well, especially with your concept. When I made this game all the way back then, I never thought the engine could become like what it is today! Definitely interested in what ideas you might have for a collaboration. Do drop me an email at yungweefyung@gmail.com :)