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?
FORTUNE'S FUN FACTS TO KNOW AND TELL: A cucumber is not a vegetable but a fruit.