Exactly what happens to the FFL yellow sheet info? Does it go into a BATF storage file? I know, stupid question but----.

They are shipped to India where the info is uploaded on computers for long-term storage in preparation for national registration.  A copy is also sent to the UN.

No, silly, they are destroyed after 24 hours, you really think goverment would lie to us.
ETA  Oops, I was thinking of the instant criminal background check

4473's stay with the dealer until they go out of business and then they are forwarded to the BATFE.

I think the dealer can destroy after a set number of years (20, 30?).

Of course we've seen that doesn't mean shit.  When the MD "snipers" were doing their thing, the cops rounded up THOUSANDS of 4473's from dealers and started calling and showing up on gun-owners door steps asking to "examine" their rifles.  It took months for some of them to get their firearms back and the cops setup a task force to find those owners that "shouldn't have guns" based on those confiscated 4473's.

Remember "Red Dawn"?  First thing they went for.

Anyone that says we don't have de-facto gun registration in this country is kidding themselves.  It's just not all in the .gov database... YET.