Guys, there's one important thing to remember here; there are other places to get master recordings of this stuff other than the actual "master" 24 track tapes. Who's Next is one of those records that has seen so many different iterations, so many releases and re-releases (a deluxe edition was recently remastered several years ago) that there are certainly a myriad of places to go for the source material.
True, there's no way to create an accurate 5.1 mix without every recorded track, but the songs in Rock Band are NOT mixed in 5.1. The game certainly is- sound effects, etc, but most of the music comes out of the front channel speakers. Rest assured there's gotta be some type of digital or analog copy in some MCA vault somewhere in the world that Harmonix can/will used if they didn't get to it before the theft. There just has to be.
It's important to keep in mind that the term "Master Recording" is relative when used for RB or GH in that it's used to separate the source recording from the actual band licensed for the game, and the covers that were created later on. I doubt that labels or individual artists would willingly hand over the genuine master tapes to some of these staple songs and let some crazy developers have their way with them. Nah, I wouldn't worry too much about this.