The brake shoes on the rear would expand out against the rear rotor and prevent it from coming off if you had the ebrake applied. The ebrake should not be applied when removing the rear disks.
With a lot of wear on the rear brake ebrake shoes there could be a lip worn on the rotor which would prevent the rotor coming off, the car would have had to have been driven with the ebrake slightly on many times for this to be the case so I doubt it. The rotor would be wobbly in this case. Rust could also form a lip. The ebrake shoes are like the old brakes prior to disk brakes on the Crossfire and the shoes can be adjusted down to clear the lip.
The ebrake shoes on the Crossfire are self adjusting for wear in a similar fashion to the early drum and shoe brakes of old.
Some cars move the pads on the rotors to provide the ebraking.
Rust on the hubs can lock the rotors on to the hubs, careful tapping can loosen them, a little rust remover can help.