This article points out that the Ultimate titles have indeed been selling poorly, down around the rate where books in the 616 universe get cancelled, except USM, whose sales are also falling.
http://comicsalliance.com/ultimate-spider-man-miles-morales-marvel-universe-crossover-cataclysm/
Perhaps the Cataclysm event was Marvel's attempt to test the interest and ability of the Ultimate titles to being readers back. So I suppose whether it returns may depend on sales of Cataclysm.
But like I said, while it may be a bit sad to see it go, the quality of the titles other than USM has fallen drastically, and I wouldn't mind seeing it come to an end, OR use Cataclysm to kill off most or all of the other Ultimate heroes and leave Miles alone in the universe, so USM can continue, since that's still a decent book, and Bendis has stated he's intent on continuing to write the book. Whether Miles stays in the 616 universe remains to be seen.