It's impossible, even in theory. When you write a file to a RAID0 volume, the odd blocks will be written to one constituent drive, and the even ones to the other. When one drive fails, you lose literally 50% of file data with absolutely no way to reconstruct them. There are no hash values, parity checks, CRCs, nothing.
About your recovery attempt... Say you do manage to recover 80% of the files from the array. How will you run a Steam game if even one file is missing from it's folder? Since I don't game on Steam, does it have an option to re-download missing/corrupted parts of a game?