What kind of mission will require humans?
until we start fielding missions which will require men.
If robots help humans discover something so difficult for robots to do (and only humans can), clever guys will design a robot to do just that.
They'll need much less time and money to devise a better robot than it wil be possible for humans to achieve on the spot, instead.
Even getting down the dark pit will be a challenge for engineers, but they'll have ideas long before humans could get there personnally.
It's a matter of motivation: a specific task has not been achieved yet by robots....but just because it's a challenge, someone will come up with the solution and do it remotely.