+2
This is a great question. They're absolutely going to try to get Nolan to keep going, but to my mind there's very little chance of that happening. Nolan's said all along he envisioned a trilogy, and he can't keep topping himself, anyway. He's doing substantial things to the characters and he's made it quite serialized, to the point at which it would become increasingly difficult to keep the story moving forward at the same speed over more than another film or two. He's also going to run out of relatively mainstream, believable characters at some point. I'm sure he could spin some of them enough to make it work, but there'll be diminishing returns to the point at which they either have to modify them more and more, abandon most fan favorites, or something else.
The only way I see Nolan going past The Dark Knight Rises is if he has a flop or two outside of the franchise and comes to the conclusion that he can buy some more faith in funding other films by returning to Batman. Which is plausible, but not something I'd bet on.
If I had to put my money on any one option, it would be Nolan bowing out after this next film, a few years going by, and Warner Bros. finding a fairly respected (or relatively unknown) director to pick up where he left off. Not another reboot, but a continuation. I don't know if it would last more than a few films without Nolan before having to go through another incarnation, but I'd like to be wrong. Perhaps Nolan's established enough of a tone and feel that even another director would be able to use it to create some very solid entries. Probably not as good, but good enough.