Once I have a worker assigned to a building, how do I remove the worker so I can remove the structure? You can't seem to fire workers and you can't delete a structure that has them. In this case I'd rather not have a stadium but an athlete is already in place.
I thought I'd share this here, to to answer half of the question in case people are still looking at this:
"A vital addition to the townscape, the building firm houses the blueprints required to replicate any of the structures sent down by the mothership. Buildings can also be deleted so long as they are not one of a kind. TRIVIA: The interiors department was founded by gifted designer Chen De'Liah."
Also, here's a screenshot from my game, showing that a message "Cannot delete the only building left" appears at the top when when I try to delete a building, of which I only have one:
So, while copies of a building can be deleted, the original cannot.
This is still true as of update 1.60 (Oct 23, 2013)