Google-apps – How to change the security settings of Google App’s Exchange protocol

Are you asking if the account will be deleted? If so, the answer is no according to Google.

Google will not delete inactive email accounts on your domain. Instead, as an administrator, you can create and delete email accounts on your domain when necessary.

EDIT: Once the account is setup, it doesn't seem like it but I'm not certain. There's no mention of inactivity other than verifying the setup here: http://www.google.com/support/a/bin/answer.py?answer=33419

Your account has been deactivated or deleted. For example, Google deactivates your account if you do not complete the steps required to verify ownership of the domain within 14 days (7 days for Standard Edition). It is also possible for an administrator at your domain to manually delete the account. In either case, you will need to go to http://www.google.com/a to reregister your domain. You will have to wait five days from the time the account was deleted before reregistering. Any data in the deleted account will be lost.

Google has this listed as a known limitation. The only thing you could do is add the nickname as a 2nd email account (not exchange) on the phone and then use that for sending email.