Finally, there is retrocession — i.e., ceding the bulk of the district to Maryland, much as a portion of D.C. was ceded to Virginia in 1846. A federal district would survive, but as a much-reduced core that contains the Capitol, the White House, and the National Mall. In some ways, this is the most attractive option. Maryland, of course, would have to agree to the transfer.
This probably is the best choice, albeit something Maryland has traditionally not been interested in. It would, however, make a certain amount of sense for Maryland's Democratic establishment to want to embrace a measure that would entrench their power.