Actually, if Hamilton & McLaren don't win WDC/WCC by 2010, I'd expect Hamilton to decide to switch team looking for his chance to get a title - by then he'd be very desperate... and, considering his flirting with Williams, I don't really think he's so faithful to McLaren. And considering his ego, I'm sure he'll be thinking McLaren is the only responsible for him not having title already (no matter how distant from the truth that might be).
On the other side, I don't think Ron would EVER admit being wrong by calling Alonso back. After Ron, well, who knows? But putting Alonso's pride in the pot - and that is another huge ingredient - I can't see whole recipe working out.
I agree completely with the first paragraph. Whilst I think what you say in your second paragraph is the most likely, a seed of doubt is planted in my mind when I think back to Dennis asking Prost to come back to McLaren for the 1994 season (although I understand Prost and Dennis' differences never sank as far as that blackmail and bribery that Alonso deployed).
I'm not totally sure what to think about the idea of Alonso coming back to McLaren. If Hamilton is still at the team, I don't think it would be a good idea. Also, there is the chance that Hamilton will improve and stop making his gaffes. If he does that, which he probably will, I'd tolerate his super-sized ego. If Hamilton, for one reason or another, was not at McLaren, I'd probably bring Alonso back to McLaren. As much as he can be underhand and arrogant, he is a class act as a driver. As with Hamilton's arrogance, I'd be prepared to make some concessions on his personality etc. to have him on board.

Ayrton Senna: WDC 1988,
1989, 1990, 1991
McLaren: WCC 1974, 1984, 1985, 1988, 1989, 1990, 1991, 1998,
1999, 2007McLaren: WDC 1974, 1976, 1984, 1985, 1986, 1988, 1989, 1990, 1991, 1998, 1999, 2008