Run Apex on Package Uninstall
The uninstall script is subject to default governor limits. It runs as a special system user that represents your package, so all operations performed by the script appear to be done by your package. You can access this user by using UserInfo. You can only see this user at runtime, not while running tests.
If the script fails, the uninstall continues but none of the changes performed by the script are committed. Any errors in the script are emailed to the user specified in the Notify on Apex Error field of the package. If no user is specified, the uninstall details are unavailable.
The uninstall script has the following restrictions. You can’t use it to initiate batch, scheduled, and future jobs, to access Session IDs, or to perform callouts.