Stitch's Great Escape's days are almost certainly numbered. The attraction will be closing for except for the most busy days in the Magic Kingdom. According to the Orlando Sentinel, you'll be able to visit Stitch in Tomorrowland from November 19-26 and from December 17 - January 2. Beyond that Stitch's future is cloudy at best.
Rumors suggest a Wreck-It Ralph virtual reality attraction taking Stitch's place, and this mostly-closure certainly leads one to believe something new is on the horizon.
I'm not terribly excited one way or another over this whole thing. I rode Stitch once and while I'm not as anti-Stitch's Great Escape as a lot of the Disney community seems to be, it's not something I will really miss. I was hoping for a Big Hero 6 attraction or maybe something Tomorrowland (the film) oriented, but I guess a Wreck-It Ralph presence won't be bad. I'm most looking forward to seeing what WDI does with virtual reality, no matter what franchise it's tied to, so cheers to that.