When the state of the art robotics is advanced enough for robots to automaously go and create factories for making more robots....
Then the only limiting factors are
a - raw materials
b - energy
Both of which are virtually unlimited in space, i.e. the moon, astroids.
No comment needed on the implications of an unlimited and cheap work force.
Secondary question - how many humans are needed (on Earth or off) to insure the species and for progress, once working becomes obsolete?
"We don't care. We don't have to. We're the Phone Company."