Thanks AGD, that article was a great read. But it didn't quite get to the heart of what I was wondering... which was what was going through Al's mind as he saw the band taking off after he left, particularly since it seems he left partially because he didn't see the band ever taking off to the point where he could make a proper living at it - and he very shortly saw that assumption turn out to be false.
I wonder if Al's ever spoken about any regret/sadness, etc. when he saw what could've been (I know he's a classy guy so he probably wouldn't ever have made a big deal about it, but it was a great stroke of luck to get the chance to return at the time he did, which was the band's heyday).
I own the Lost Beach Boy book and need to re-read it too though, as it might answer some of my questions.
He never mentioned it as regret to me, it was more like slap your head stupid...you almost blew it! The main thing Al told me was that the other guys took a long time to forgive him for it. In fact some of the other friends and family have told me the same thing, Al was generally held in a lower regard because of what he did. And of course Murry
never really forgave him. When Brian wanted Al back Murry set the terms, "no partnership, no royalties." He set him up as a sideman. David on the other hand thought of Al as the guy who saved the day when Brian decided to not tour, he was blown away that Al could step in and sing like Brian and play the bass. He called him a hero.