Annex it back into Maryland and keep all the government stuff in New DC
Maryland doesn't want that, though.
You imply the federal government cares about that
New states may be admitted by the Congress into this union; but no new states shall be formed or erected within the jurisdiction of any other state; nor any state be formed by the junction of two or more states, or parts of states, without the consent of the legislatures of the states concerned as well as of the Congress.
If you're doing junction, you need approval of the state in question.
Virginia actually wanted its half of DC back, which is how it got its half back. You can't shove DC into Maryland without Maryland wanting it.