I suppose I'll get judged by making this comment, but I do think that if the "wife's and managers"(not just Brian's) stayed at home, Mike, Brian, and Al could probably end up communicating again in a friendly way. I think that if they went back to being just the core group without any outside elements things would be a lot less complicated and less tense.
Maybe it would be friendly at first, but of course that description casually ignores the likely scenario that things could once again become toxic in terms of the relationship between Mike and Brian. Not to mention Mike and Al!
If one believes that Brian is truly not at risk for being pushed around due to wanting to avoid confrontation, I suppose it's easy to think that minus the spouses, that everyone's relationship would "magically" go back to some good, non-toxic, healthy place, and that lots of great music would be created.
That, of course, ignores Mike's penchant for vindictiveness at not getting what he wants, kicking out founding member Al Jardine, effectively significantly contributing to Van Dyke Parks leaving the scene, Mike's crass reaction to Summer's Gone, Adult/Child material, blowing up and walking out on sessions for Old Man River, I could go on and on and on. I'm sure there are countless other incidents that have not been made public.
Mike has a long, documented history of rolling his eyes at much of his cousin's more interesting ideas (when Brian dares to explore beyond lame rehashes of old BB tunes), and while Mike decades ago definitely showed he had the ability to also write sensitive and quality lyrics, there's no reason to think that Mike's toxic, ego-driven behavior won't still rear its ugly head again nearly as soon as "pesky" spouses are out of the picture.
Mike does not appear to be as sensitive as he should be with regards to a very sensitive person. He has acted in all sorts of very uncool ways towards his bandmates during periods of time long before Melinda Wilson was in the picture, so really this is not about spouses. This has happened repeatedly, over and over and over again, without him taking responsibility for having acted regrettably towards his family or friends. Brian publicly called Mike out about the super lame Redwood incident where Mike guilt-tripped the crap out of Brian in Brian's book. Mike remains silent and unapologetic on the matter. He doesn't seem to ever properly acknowledge Brian's illness in any meaningful way beyond just solely blaming drugs.
Why does Brian, at his age, need to deal with this crap, or even the potential for it? If you really, truly believe Mike does not suffer from an empathy problem, maybe you can convince yourself it's a good idea, and that they'd get along "better". But take a look at the big picture, and based on historical observation, it doesn't seem likely that things would ultimately wind up in a good place.
Plus, now you are dealing with people who are getting to an advanced age, and extra stress/drama is really *not* something that Brian needs to even "maybe" deal with at this point.