After 90 days of inactivity, all subscriptions for the user are removed (deleted). They will not be restored if he logs back in after the 90 day expiration. The theory being that if the user hasn't visited at least once in the last 90 days, he's no longer an active member and chances are the subscription emails are going to an invalid address.
As long as you visit the site (and log in) at least once every 90 days, all of your subscriptions will stay active and not be deleted.
Since you average 3.51 posts per day, I don't think you have anything to worry about. ;)
Director, Applications & Support Services
Wiley Publishing, Inc.