The exact same thing happened to me at PIT. Everything OP described happened, except the outcome was that the aircraft itself moved to an unused gate (area walled off at B concourse, I think we were allowed off at B41). Now looking back, it was sort of neat getting off in an abandoned area, but no fun at the time.
Oh, we were late at night there in the first place, because of the delay caused by... PHL (it was PHL-PIT flight).