I'm somewhat hoping I could get it powered up and use it, but I imagine there isn't much hope at all for it.
I read some guides online, and noticed a few that mentioned vinegar could remove corrosion. I disassembled the S2 as far as I could, and then just dropped it in a small container of ACV, and plan to leave it overnight. There was a good bit of bubble activity when I left, so I assume the vinegar is doing it's work on the corrosion quite nicely.
I'm not really expecting the phone to work at all, but who knows. As long as there isn't any physical motherboard damage and no short-circuiting occured, I would think it would be fine.
As for what happened to the phone, I assume it was dropped, but it's possible it was ran over as well. Ideally, I'd hope the phone was just dropped and the battery came out instantly to reduce the chance of short circuiting.
My plan for now is to just let it sit in the vinegar for about 8 hours, and then check on it in the morning. Depending on how much corrosion is left, i'll either just try to clean up the rest with a tiny brush, or just let it soak some more in fresh vinegar. I'm hoping the vinegar itself doesn't damage anything crucial though.