This seems to be a request that was just asked on another thread, but technically, if the person knows just enough about the billing info, they could get ahold of support, and claim that the 'old' admin is no longer with the company, and that they now need admin level access. Support doesn't verify that 'firing' so it could happen.
I've seen it happen once when there was bad blood in the company. They kicked out one of the owners.