But if they remove marriage from the equation, how is that trying to define it?
Right now when couples separate there's a legal mess (particularly if children are involved). That legal mess doesn't change whether or not there's been a marriage. There are still questions of support, property separation, and child custody.
It’s no different from asking, “what happens if they were to suspend Habeaus Corpus.” They can’t suspend it and they can’t change the definition. They can only protect it.