I doubt Schumacher would go anywhere other than Ferrari, so that is completely moot. The only former champion that McLaren can get is Mika, but with his retirement from DTM, it seems racing for him is over. IMO, McLaren will end up with Sutil in the team. I'm not sure what is going to happen to Alonso and that's key to all this, but I can see RedBull as a very possible alternative...according to some reports, Alonso has already passed up an offer from Toyota, and as much as some of you may like to fantasize, he is not going to Williams. They simply won't spill the dough for it. RedBull though, they already use Renault engines, so it could be a possible stepping stone for him going back to Renault later.
Now, as far as him going to Ferrari, I find that complicated. There will be a spot there only after 2009, and that's if Kimi retires, which btw, Alonso also said that he planned to retire by the same time as Kimi. At the start of the year, he said his contract with McLaren was probably the last contract he was going to make...of course everything went downhill this year with the team, so now he needs another team, and that's why he's probably looking closely at the options, cause he needs a team that can give a fighting chance at the title for the next two years. Another complicating factor at Ferrari, is he doesn't really like the team. I remember at the end of 2006 he saying to the Renault guys: "I don't mind which color you guys paint the car for next year, as long as it's not red". So I think it's an unlikely partnership.