When TSR (maybe it was already WOTC owned) re-did 2nd edition books, you didn't have to BUY them. The rules were the same. I had the old-cover 2d ed books beside the new cover books (like High Level Adventures and Combat and Tactics) and it worked fine. The same should be true here.
I recently ran my latest D&D group off (just wasn't working out), but we had been gaming 3d Ed. I still like 2d ed better.
I've read all the pluses and minuses, but the one big thing they should have done - CHANGE THE MAGIC SYSTEM, STUPID - was not done. Most folks like the increased character flexibility 3d Ed. gives. I don't. A wise 2d ed. DM with all the books can find or craft a kit appropriate for the character. And dual-class rules need not be etched in stone.
Anyway, I'm sad to see the change too. I just spent money on PHB, Tome and Blood, Masters of the Wild, and Song and Silence.