アップルエンタープライズ FAQ から:
Distribution provisioning profiles expire 12 months after they’re issued. Two months before expiration, the iOS device begins displaying notifications about the impending expiration. After the expiration date, the app won’t launch.
Before to a provisioning profile expires, use the iOS Development Portal to create a new profile for the app. Create a new app archive (.ipa) with the new provisioning profile, for users who are installing the app for the first time.
For users who already have the app, you may want to time your next released version so that it includes the new provisioning profile. If not, you can distribute just the new .mobileprovision file so users won’t have to install the app again. The new provisioning profile will override the one that’s already in the app archive.
ソース: http://help.apple.com/iosdeployment-apps/mac/1.1/#app43ad802c