At the time of the Lucifer rebellion, the planetary prince, Caligastia, would not let any souls leave this planet for a couple hundred thousand years - they could not advance to the mansion worlds which circle the planet Jerusem, so teachers came to the astral realms instead, to guide them between lives.
from what world according to the Urantia Book did these teachers come? Or what were those beings?
"The astral realm is where souls recuperate between incarnations. At the time of the Lucifer rebellion, the planetary prince, Caligastia, would not let any souls leave this planet for a couple hundred thousand years - they could not advance to the mansion worlds which circle the planet Jerusem,..."
After its failure, why wasn't Caligastia removed from Earth like the other rebellious beings?
probably one of the heaven worlds as covered in the UB would be my guess. Now that this planet is being freed we won't need the astral.. I was moved to around the moon in the meantime to protect the folks there from nuclear war and such. In time there we;ll be less and less astral... 
the other rebellious beings were brought here and are still here. This is their prison ward... those who did not "repent" will be gone with the reversal. Lucifer was removed when Christ walked this world... and Satan 700 years ago at the time of the renaissance. Caligastia just mentally broke up... and I suspect some others did too. If they had been removed... Christ would not have needed to come in that sense...
This world has a special purpose... which is to "save" it.. so other failed worlds from failure of Adam and Eve missions do not get blown up. for failure of life. This world could have become another asteroid belt... this is the great experiment... how to restore failed evolutions. Orvonton is famous for its grace.
I think Nebadon has had only 3 rebellions against the celestial government.
