As far as I know, although Square Enix has stated that there is another year's worth of content planned, that does not mean that there will not be more content planned even after that. They've already stated that as long as people continue to play, they will continue to support Final Fantasy XI. In fact, as far as I've seen, there's a fervent denial from the company that the release of FFXIV will in any way mean the end of development for FFXI.

That said, I don't believe that they're going to be able to get to everything. Every story has its diegetic world--the world we're told about but never actually get to experience firsthand. It's part of what allows a story (or in this case, a game) to immerse the reader (or player) in the world. It gives hints of something grander, even if that something grander isn't quite so fleshed-out as we might like.

That said, given that both Rise of the Zilart and Chains of Promathia share a final mission, I expect that they'll tie at least that loose end of before FFXI really ends. I do expect that we might get one more full expansion, although I don't imagine it will be quite so expansive as any of the previous ones (I'm really rather hard pressed to say that any particular job is a necessary addition at this point). We're not going to get to experience everything, of that I'm almost certain, but I think calling this the end is somewhat premature.