Why's the ending so hard to believe they let him do that? It's not like any of the new writers will have to adhere it. I took it as like Morrison's alternative Batman Beyond universe or his now alternate apocalyptic future. More like a glimpse of possible futures for those characters rather than definitive ones. I didn't think it was a big deal and a nice treat to bookend his run. Plus he's Geoff Johns...I don't think he gets told "No" that much from DiDio.
The future of the characters is "far" in the future though. There is nothing ever going to be written that says any of those glimpses of the future will not happen.