Do a quick format if anything, that way the index is only wiped.
After that go to Stellar Phoenix and get their FAT32/NTFS file scanner, and scan the flash drive (post formatting), it'll list the files you'll be able to recover. If the results are satisfactory with you, you can restore the files with any data restoration scanner out there. Or bittorrent Stellar Phoenix. (It's worth every penny tho).
Quick Format so only file index is wiped.
Stellar scans every fragment and sector and rebuilds the index on its own. Stellar will not alter or write to the targeted drive in any way, the index is stored in memory and you can save it to another path.