Think of franchise histories. Vin Diesel backed from "2 Fast 2 Furious" and "Tokyo Drift," but the franchise is still running smoothly after his return in "Fast & Furious (2009)." Considering "The Bourne Legacy's" healthy global take, Renner has enough clout to maintain the franchise on his shoulders until Universal makes bigger plans for a sixth installment. After all, a starless "Tokyo Drift" made almost $160M back in '06, a much less international movie market at the time.
Pure speculation, of course, but the Bourne franchise is not (yet) dead without Damon and Greengrass, and I believe it will maintain course until it is wholly necessary to bring them back...which would be if "Bourne 5" were a total domestic flop.
Universal will keep this potentially lucrative concept of a "Bourne team-up" between Aaron Cross and Jason Bourne on the backburner as long as they can, in my opinion. It's one of the few genuine cards they have left to play regarding this franchise, and the market for team-ups (post-"Avengers") makes the Bourne team-up valuable. Reap in remaining, diminishing revenue on "Bourne 5" and shovel in a boost with a "Bourne 6 team-up" with Damon's return...how is that a bad business plan?
All this to simply say: Bourne 5 is Renner's, and will most likely stay that way.