[RnMomof7]

No. If they later on UN-defected, then they would have to regularize their marriage. Otherwise, what do they care that the church thinks their marriage is invalid?

If the couple NEVER seeks an annulment and they continue in the marriage, and there are "irregularities" are they living in a state of fornication??

[Mad Dawg]

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.