If you continue to rent it; you continue to report income and expenses, including depreciation, on Schedule E. if you later sell it, it depends on where you are on the 2/5 year window whether you could still exclude part of the gain.
@Carl - whether the owner gets a full or partial home owner exemption depends on when the unit was rented. If it was only rented after it was used as his principal residence, he gets the maximum exclusion. But if he occupied the unit, as his home, after previously renting it, he has to allocate the gain. In addition, it's only "non qualified use" after 2008, that is prorated
