I think the right answer is,”Possibly.” I know some disagree with me but I tend to have the paradigm that if you want to KNOW your marriage is valid, you play by the rules. But one can’t be sure that one undertaken otherwise is invalid.
Of course the one who “defected” is probably in a state of mortal sin anyway, if only because he’s not going to Mass on Sundays and Holy Days of Obligation.
What are the rules????