Activision has announced it's plans to make all those Wii Guitar Hero Rockers happy. Either you wait for your disc to be replaced, which could take 4 - 6 weeks, or you can send your unit back for the full refund. If you decide to send your game back for the full refund you need to follow this link. Read it very closely and follow all the directions for a full refund.
But the real question is, why not just keep on rocking and wait for the replacement disc? If that doesn't work, then refund it, but at least give the game a chance.