Just thinking out loud here, but once the tax stamp came in, wouldn't it be difficult to transfer the gun to anyone else without the cooperation of the person whose name (or trust, or corp)is on the stamp? If he (the dealer) absconded with the weapon, what could he do with it? If a dealer had several stolen nfa items I feel he would be sought after by a couple of alphabet agencys. In a bankruptcy wouldn't the trustees be compelled to release the weapon to the buyer? I could see some issues, but unless he disapeared I would suspect you would get your items eventually.
Nos operor non pensio volutabrum
(We don't rent pigs)