In date of sale, enter when it was removed from service as a rental.  Yes, on real property you get depreciation on the mid-month basis.

Do not enter a sales price.

Keep the depreciation schedule showing the accumulated for as long as they own the property - you may need that info down the road.

You can also maintain the asset(s) by changing the Form to 17 (F 4562 only) to the info stays with the file when you proforma - but after the return is finalized.