He has already been charged with the crime so the warrant can stay active forever. Many states will not extradite for a misdemeanor but will simply leave the warrant active. It will continually cause a problem and if he gets stopped in a state that Mo IS willing to extradite from, he's toast.

Obviously if he ever goes to Mo he is subject to arrest for the warrant.

I would plan on this happenning every time he gets stopped for anything.