First, I hope that they don't. Android is much less open than people seem to think. Only at the moment of the release we knew what features Gingerbread has, for example, and it was only some weeks ago that it was unofficially confirmed that Gingerbread was 2.3 and not 3.0. I dislike a lot the way they act, branching upstream stuff and creating problems for themselves and upstream itself in the long term. I like the way Nokia is handling community stuff with respect to "we add it to upstream first". I think is not only polite, but very wise. I've maintained 2 super-small packages in Debian, and even there I realized how important is to do work upstream so yo don't have code bases that diverge.
Second, I think they will not use switch to Android after all this. Nokia has invested a lot in Qt, MeeGo and Symbian, and their employees have the know-how, experience, etc. They also have a different set of services, so it doesn't make sense for them to compete with Google in their own field, where they have advantage.
Also, one of the things that I like of MeeGo, it's the use a completely standard X11, libc, etc. That allows MeeGo to be capable of reaching from phones to desktops. It also frees Nokia, Intel and all the MeeGo contributors to develop on their own their stack.