Let's get this part out of the way. Yes, this is kind of silly. No, it's not really analagous to the CIA destroying the Watergate tapes. Yes, Congress should have more important things on their plate. However...if you happen to be a fan of the NFL and a fan of integrity (probably doesn't hurt to have an irrational hatred of the Patriots either), you've probably been wondering yourself how that investigation could have ended so abruptly. I have no idea what becomes of this but Goodell better spend some time with The Purple Jesus and learn some of those spin moves pretty quickly because unless Congress let's him off the hook, the line of questioning looks pretty easy to me.
Show the tape of him speaking to a National TV audience proclaiming that the original penalty was only for the infractions in the Jets game and that they are going to collect all of the evidence and the Pats are subject to further and more severe sanctions if any more wrong-doing is found. From there, it's easy...
Congress: Why did you destroy the tapes?
Goodell: Because no more wrong-doing was found.
Congress: Then why did you destroy the fucking tapes?????
See what I did there?