Consider yourself lucky that the disk went and not the memory card.
I left my GT3 in Boston while I was home for winter break, but I remembered my memory card thankfully and I had a "backup" GT3 that I bought for $10 just for the different color box art. Somehow, though, that disk is actually Spiderman...I am not joking, it is a Spiderman DVD with a real GT3 label...fused on. Apparently it fell into the wrong bin at Sony and got packaged as a GT3 disk. (People have suggested selling it on ebay as a collector's item.) Anyway I was upset, but as long as you still have your game save, all is well.
That's why I back everything up onto a second card every 5%...and when I get to high percentages, maybe even a third.