Having fewer episodes might actually help the show last longer, too--if it's not as expensive to produce a season, why not make more for syndication and to sell to international markets and whatnot, you know? I'm not an expert, so I really have no idea how all that works, but I don't think CSI will get the axe unexpectedly. (Miami was a bit of a shock, especially since New York lasted longer--NY had several years of warning before they got cancelled. Speaking of NY, they got 18 episodes in their eighth season, and they got another season of 17 episodes before being cancelled.)
I certainly hope we get some warning before it's ended. I think it's premature to assume this is a sign that the show's being cancelled, when there are so many other elements to consider (including CSI: Cyber being put in the same timeslot). I'm not saying it's not a possibility, but...we can only wait and see. Fingers crossed, I guess. I'm not ready to let go!