Electronic Arts announced that due to the licensing contract’s expiration, Rock Band and Rock Band Reloaded for iOS will be removed from the app store on July 31. If you are a user of the game then you likely already received a notice that the apps would be removed. If you own a copy of one of the games it will still work after July 31 but you will not be able to purchase new songs after that date. Previously purchased songs stored on your local device or backed up on iCloud would still be playable.
Source: The Verge