When a flight comes in on a normal stand, you can't delete it.
When a flight comes into a remote stand, it is still possible to delete the airside bus stop, but the plane will be stranded on the runway.
It is not possible to reinstate a new airside bus stop - as a plane has been assigned to the stand. Closing the stand is not possible either, or removing the plane.
Did not save the bug as I shut the game down without saving. However, it should be possible to recreate it.