Apparently Kirked penned a letter in the latest comic saying that he thinks the show could go till at least season 10, if not longer. He also said that things start to really pick up around season 10.
David Alpert has also apparently talked in the past about wanting to continue the show to season 11 or even season 12, and that they have milestones to address if they are able to get that far.
This is all dependent on ratings, which as we all know haven't been the greatest these last couple of months. I do believe we could get to at least season 10.