As surely as the sun will rise tomorrow, we'll get a new, updated GTA coming out in a few years time. It's just an inevitability at this point to be honest. The only thing that would stop it would be Rockstar going under, which isn't likely to happen any time soon, a industry wide crash like we saw in the early 80s, which is unlikely despite what some analysts claim, or Rockstar being bought out by another company, and even then they'd continue the making of GTA just as its such a gold mine of revenue.