Why is the depreciation unused? Are you selling the property? Are you converting it to personal use and moving in to use it as your primary residence now? It matters.
If you're selling it, then you have nothing to deal with on unused depreciation, since all previously taken depreciation is recaptured in the year you sell it, and you pay taxes on that recaptured depreciation in the year you sell it.
If you're moving into it, then the previously taken depreciation is held and suspended "in limbo" until you do sell or otherwise dispose of the property.
