Technically, one of them is still XX, and one is still XY.
Seems to me Michael doesn't exist anymore, and so Michael's marriage is over. Void. Non-existent.
If one of them grafted a tail onto their bodies, would that make this an interspecial marriage?
Surgical impersonation does not change the essence of what God has made.
A name change does not void a marriage, nor does sexual mutilation. It as real a marriage as ever, even if they are wierd.