If Brian were to decide to hang 'em up and quit with the touring, I'd get it. I'd miss him, for sure, but I could see why it might be an attractive option for Mr. Wilson. He'd miss out on the money any tour might generate, and there's the lost opportunity to promote any current material to consider, as well. But I get the impression Wilson has never been entirely comfortable playing to the public (to say nothing of the constant travel touring demands out of a person).
That said, I hope we
never see the day where Brian Wilson decides he's no longer interested in writing and recording. Can you imagine?!? Now,
that would be the biggest loss, I think. As long as the muse is with you, Brian, please keep pumping out those studio productions.

----------
Now, all that said, the one circumstance I'd
definitely want to see Brian on stage for again would be another reunion of the surviving Beach Boys. I'm just conjuring this out of thin air, but something like say, some kind of Beach Boys joint-celebration of the
Pet Sounds/
Smile era, would be absolutely incredible. Seeing, for example, the Beach Boys performing all of Pet Sounds during the first act, with the BWPS-styled Smile tunes following the intermission? That would be so Won-Won-Wonderful, and I'd be crushed if everyone but Brian were to sign on for something so very cool.
Shame it will never happen.
----------
But back to recording... Who knows? Maybe (just maybe) the 'Boys will find it in themselves to reunite long enough for one more studio album?
Don't get me wrong: I fully recognize that
That's Why God Made the Radio is a fine way for the group to bow out; ending things on a very high note, and all that. But I still very, very much want to hear a completed
Life Suite (preferably sung by the Beach Boys) one day. That, and, for all we know, Brian and Mike may even have some more terrific tunes up their sleeves?
As much as I adore TWGMTR, if we could get the remainder of the Suite, coupled with some more new Wilson/Love material, I'd be awaiting
that release with baited breath.
----------
But even if -- as most suspect -- the band never does get back together again, I'd still be very interested in future solo albums by the guys in the group. A follow-up to
No Pier Pressure, for example, would be most welcome.
----------
So, the TL;DR:
"Don't leave us, Brian!"