My ( now ex ) stayed in for a couple of years after I left & it put enormous stress on the marriage.
In fairness it isn't great for the partner who stays a JW. In our case - one minute she was married to an ( ostensibly ) strong elder - next minute she is married to an "apostate" and constantly , every meeting , she gets faux sympathy from the other sisters and told "how well she is doing" etc. Her status changed overnight from being part of a successful JW family to another "single" sister with an unbelieving husband ( pretty much the lowest level in the congregation ) and she would come home from the meetings resentful and angry. Its a hugely divisive situation.
Eventually it all fell apart & she left ( and then left the Org after finding a replacement "worldly" guy. ) Unless both partners leave together - it's not a great scenario for a happy marriage as so much of our lives as JWs were built around the Org.