So, the real question is, when will he NOT be the GM? He's already mentioned that if any other GM did as poorly as he has done, he would have fired them. But, he still sees no reason to step down. So, it's safe to assume he will be the GM until he no longer maintains the mental and physical capability to do so (and probably a couple of years after that point).
Jerry was born October 13, 1942. That makes him 70 if my math is correct. He could very well be, or try to be, the GM for the next 15-20 years.
With that, the next logical GM choice would be his son, Stephen. Whenever he is allowed to take over, the next pertinent question is, "Will Stephen run the team like his father?"
Perhaps, perhaps not. By then, the NFL will probably be a very different league. The only thing we DO know is there probably won't be any of the current players still on the roster - unless they are coaches.
Now for the ultimate and most pertinent question: can YOU as a Dallas Cowboys fan wait out Jerry Jones' tenure as GM? In other words, can YOU weather the storm of years of continued mediocre results, vast criticism from family, friends and other Cowboys haters, and last but not least, the thought that Jerry Jones finalizes the completion of becoming the next Al Davis and the Cowboys become what is now known as the Raiders?