It wasn't just a license deal.
Viacom owns the Turtles lock, stock, and barrel. (I went to Mirage's web site, and they say they won't do Turtle stuff anymore because they sold the rights.)
With so many conflicts over rights for the Mirage stuff (apparently, Eastman and Laird had a falling out, which is a shame. Two buddies who hit the big time, and something like this happens. This is why I'm so glad my self-published stuff is entirely owned outright by me. I may not be the best artist, but at least the arrangement doesn't breed animosity), both as far as the original creators and those who made additional stories, we may never see anything but the Viacom stuff (or the original cartoon, for those of us who thought it was great).
So, for 2012, here's your new Teenage Mutant Ninja Turtles....