As long as people keep paying for them, Bethesda is either going to keep making them, or at least contract them out to someone else to make them. I can't picture the business end of the company allowing the product name to just "go away" without trying to either milk it to death with cheezy "sequels" cranked out in quantity or selling off the fanchise for a heap of cash. What are they going to do, tell us "We decided that we'd rather concentrate on trying a RTS space game, so we're dropping the TES story"? Not a chance.
On the other hand, the shift in emphasis from primarily a RPG with a crude combat system to a FPS game with some RPG elements shows that the series may not stay as it is. Once upon a time, in a "fairytale" story about business and entertainment, a buch of programmers wrote a game called "TES" because it was what they wanted to do. Now it's a large corporate entity, with bills to pay, employee payrolls to meet, and stockholders who wil be perturbed if it doesn't show a profit for more than a quarter. Bethesda isn't going to give up on TES anytime soon, but it just MIGHT eventually evolve into that space RTS over the next 3-5 games if that's what marketing says will sell.