I don't think that there would be a big impact even if Nokia left Qt alone completely, since it is the base f.e. for the KDE desktop environment, so there are many people from the open source community who are actually eager to continue developing Qt. That's nothing we should care about right now.
Of course there are also guides on how to migrate from MFC to Qt, and how to use both at the same time, so this is not much of a problem either. Getting started and doing the actual conversion is...