It was only recently that I installed Oblivion on my HDD, before that I'd play hours upon hours from the disk, My disk still works and my Xbox still works, I'm pretty sure these games are designed with the game not being installed to the HDD in mind. I wouldn't worry about the disk "dying".
this
i rarely install games on my 360 (only have an old 20 gig so i need every bit of space i can get) and ive only had 1 game disk 'die'
and that was because my 360 tipped over and the disc reader went bat [censored] crazy and etched a crop circle into the disk