What happens to my data when I uninstall Shared Contacts for Gmail®?
Shared Contacts for Gmail® does not keep any of your personal information or information about your contacts in its database.
During the synchronization, the application just cache the contacts that are share and modified and none of the contact data (names, e-mails, phonenumber etc..) are stored on the application database.
Therefore, when you uninstall the application, every user will still see the shared contact groups and shared contacts in their Google Contacts Manager, but every change they make will not be synchronized anymore.