Ok...
Got an idea how to try to find your song file. I tested, it worked for my recently saved BIAB files.
Assuming you have Windows 10.

1)Click Windows logo + E (explorer window will open)
2)Just scroll DOWN, you will see "RECENT FILES" list on main page.
3)See if your file(s) is there.

I can see my files that I saved in BIAB recently...

Good luck.