It's hard to say. I know Michael and Vanessa are working on the show as well, but I don't think they want it to be their forever job, otherwise they would be inheriting the franchise from their parents. If Ross and Janice are looking to sell, and their kids don't want to be dedicated to it forever, it's hard to tell if any of them will still have a part to play in the production of shows, etc.
Time will tell if they do end up selling, but at this point in time it's still reportedly, so there's been no official word. It's just crazy they'd want to sell Alvin and the Chipmunks after what happened with Universal Studios! I heard the quote a few times tossed around said by Ross Jr. (though I can't find the original source of it) that his dad would "return from the grave" if he ever went ahead and sold the franchise! Age related reasons I can understand, since Ross and Janice are getting on in their time, as sad as it is, but I can't grasp on any other reason outside of that. Ross and Janice have always been so protective of these characters! And even with Michael, he didn't really care too much about Alvin and the Chipmunks at first, but when he saw how much they meant to the fans who enjoyed it, that's the only reason he even helped with ALVINNN at all - because of the fans. I just can't see Vanessa and Michael ditching them so soon, but who knows.
But they're apparently selling now? I wonder if there could be more than meets the eye with this, because we don't actually have the whole story yet...