People really need to get off this thinking something is "on" a form x. Items transfer using a particular form, they are not "on" any form. That said, unless the dealer was arrested for some crime, the transfer can still be completed since he still has it. If the FFL expires, NFA inventory that is not a post dealer sample simply moves to personal possession if the dealer is a sole proprietor, it can be more complicated if it's a corporation. If his FFL is still active the transfer simply goes on as usual, ATF does not care about the bankruptcy proceeding. You'll need to make contact somehow to figure out what the status is. A storefront closing has no effect on the transfer process.
Bankruptcy comes in multiple flavors, and assets may be sold to pay creditors, but if you can prove you paid for the item then it's not his asset to sell. Now, if he never filed the transfer and you have no receipt, you have a whole different problem.