I'm so sorry to hear your save got deleted!! Unfortunately, I don't think there's a way to recover it; if you were stuck, I might be able to help, but as far as I can tell (after booting up Polymute again for the first time in years and testing things) it's probably been overwritten. For what it's worth, a lot of the puzzles are fairly quick to redo if you can remember the solutions, though that's not much consolation I'm afraid.
All good, I figured that might be the case. I feel like I need to put out some sort of PSA for indie devs to avoid this sort of thing, cause this isn't the first time I've run into it lol.
I wound up just starting from scratch, and the silver lining was that I was able to take better notes this time of what to come back to, so that was nice. Just rolled credits! I missed a couple of the tablets, never really pieced together what they were for, so I wanna go back in and do that. I get the impression there might be a True Ending if I do? Anyway, I'll definitely have plenty more to say once I'm fully done with the game, but I wanted to let you know that I stuck with it and I'm glad I did!
I'm glad you did too!! And yeah, in my more recent games there's a little more friction to stop you from deleting your save altogether, so it's something I figured out eventually!! I do seem to recall something wrt the tablets, though there's also a secondary thing that I won't spoil, which is more complicated (though other folks have figured it out and posted about it in comments iirc)