When Apple launched iTools, they didn't offer itools.com addresses, but mac.com ones.
I therefore don't believe they'll discontinue those mac.com addresses (that would be very foolish IMHO).
However, I doubt very much that they'll offer mobileme.com.
Instead, it would make more sense to keep offering mac.com as they have always done and bring a new address that will work alongside it like, say, iphone.com... I don't know how long they've owned iphone.com (they used to only have iphone.org), but www.iphone.com
reroutes to Apple, so it's definitely a possibility and much better than mobileme.com! :-)
Also, it could entice people to get both mac.com and iphone.com addresses, making Apple earn an extra $10 per user.