Hmm, sounds like your mom has to make some tough decisions.
- does she want to live with this man, or not?
- does she want to remain married to him or not?

I think the answer to those 2 questions will help her sort out how to set things up in the future. Unfortunately, she needs to make these decisions soon. Making NO decision IS a decision - to live with him for the future, "until . . . . ."

It may be difficult for her to decide that she does not want to live with him; she will wonder and worry where he WILL live, and really that should not be her concern. But I think it is normal for her to wonder like that.