If you start seeing some songs disappearing from the Rock Band store, what you are seeing is our intellectual property system at work. The licenses for some older Rock Band songs are starting to expire.
Obviously, Harmonix is looking to extend what licenses they can, but not everybody will be willing to play ball. As a result, certain songs will no longer be available to purchase. If you have already purchased the songs, you have nothing to worry about, but anyone who is still looking to pick up Rock Band downloadable content should finish up their collection soon.
Metallica Pack 01 which included “Ride the Lightning,” “And Justice for All,” and “Blackened” has been pulled from the Rock Band Store. Harmonix promises to keep its fans posted if any other songs drop.
"We'll post as more information becomes available, with re-licensing updates likely coming in on a quarterly basis," Harmonix said on their Facebook page. "We're hard at work to minimise the impact on the RB catalogue and RB community, securing extensions for an overwhelming majority of content and, most importantly, making it a priority to give you advance notice if songs are expiring and have to come down."
Just don't pull any Justin Beiber songs! We'd hate that!