I think we should simply take their names, process their overt request to renounce their citizenship, revoke said citizenship, and immediately deport them to a neutral 3rd country such as CUBA.
Strip them of all assets due to their violation of the 14th amendment's provisions of their being a non-person having supported insurrection and/or rebellion making a government debt due to confiscation of assets null and void.
Shoot them in the face if they attempt to re-enter the United States. Issue letters of Marque to anyone who asks so that we can sink, shoot, and set ablaze any and all boats, ships, dingies, or rafts they may board with an intent to re-enter the United States.
In short, to hell with them.
But they are already an independent republic. Shouldn't we simply recognize that fact, and start the process of restoring our Constitution?