The fact that you regard "saving a marriage where one partner is in your view 'too dysfunctional to hold onto him/herself" as a higher value than achieving differentiation probably means that you have FOO issues that are causing you to fear failure more than fusion.
Unless a person suffers from an untreatable medical/chemical/personality disorder, I do not believe there is such a thing as a person who cannot hold on to himself, nor a marriage that can’t be saved. It might be that one of the people is actively blocking recovery, whether conscious or unconscious, but I think all people can eventually learn to reprogram their perceptions and their reactivity to a point that the marriage can be sufficiently healthy. Maybe not perfect. IT might take a long time too, longer than one or the other is willing to wait.
My FOO issues do not come into play here as this is purely a value judgment to be made by each person. I do not consider my marriage to be in the camp of needing to be saved at the expense of my personal growth. Nor do I have an unlimited time horizon. I do have my parameters and at this point I am willing to let things play out in favor of the marriage. At a certain point in the future, this will all change.
