Did you notify them? I would keep them admitted, scince their application was already accepted, but include a suspension.
1 month inactivity --> Suspension.
1 year of suspension --> Removal.
Either way, there should be a gradual kind of system. This seems a little too rigid.
Also, they would have to notify Clan staff for a "vacation" status, which means they can be inactive w/o suspension.
Review my build yet? :3