I really highly doubt that CSI Miami would ever be able to continue without Horatio Caine or David Caruso. As much as people may make fun and mock David and his character, but Horatio/David is iconic for this show, he is the lead, the foundation, and if he falls, the show falls with it. People can deny it but it's the simple truth. This show falls and rises on the back of David Caruso and Horatio Caine, once we lose them, CSI Miami is done for without them.
Look at what has happened to CSI LV since Grissom left the show, that viewership took a dip at about 25% when he was gone and it still hasn't recovered and probably never will recover. There are some characters that are the heart of the show, you take that away, you are killing the show.
Sure CSI Miami may drag out a few years like CSI LV is doing, but without David and Horatio, it just won't be CSI Miami anymore. And I doubt the networks are that stupid to do something like that unless they just want the franchise to break up and fail.
All in all, I'd be really shocked if David doesn't return for next year.