Would like to preface this by stating that the output produced by classic Van Halen hasn't diminished with age one iota, and I dig the music just as much now (if not more) than I did when it was first released.
Don't really think it matters if Hagar bails and Roth comes back or not, in terms of making Van Halen a band with a viable, creative future.
The way I see it, the opportunity the classic four had to put it all back together and move forward with integrity in 1996 was shot to shit (no two guesses who bears the brunt of the responsibility for that, either). There won't be another chance like that again, and if the aborted 2000 reunion demonstrated anything, it's that these guys can't get it together. For seemingly petty reasons to us on the outside, but there it is.
Ed.........well, he's just befuddled. Just an example of Nero fiddling while Rome burned. Alex has stepped up as the de facto leader for Van Halen. Both Ed and Al have been cocooned in fantasyland for too long (where half-filled arenas and three new song releases in 6 years are an indication of a successful, legendary rock band), and the shuttle won't be landing back on planet Earth anytime soon.
Classic VH required all four members firing on all four cylinders to work. Roth alone isn't enough to make the band rise from the ashes. It would take attitudinal and artistic changes on behalf of the others to get the Phoenix airborn, and those are concessions the Van Halens aren't even willing to admit to, never mind make.
About the only possibility I can see, realistically, is a reunion tour of oldies. Probably not played at 100% of what the band was and is capable of, either. Would be a cash grab more than anything else. For some that may be fine. I can understand the need to take a classic VH reunion however you can get it.
Regarding my own expectations based on the standards the classic lineup set for itself and the fans in terms of quality, content and performance, the scenario I described isn't gonna cut it. Not even by a long shot.