RAT deployment is gravity/airflow only so may well have been compromised (think a non-deployment of a CRJ ADG happened once during testing in about 20 years but it hadn't been stowed correctly - unlike normal operations the ADG was routinely dropped for access).
AFAIK the APU will start & run over the entire envelope but just can't be guaranteed. Again from testing, you get some residual Hydraulics from the Reservoirs (my memory is up to about 40s but, as I said, the more you use the controls, the quicker the pressure dissipates).
On the CRJ you would retain some roll control via the Spoilerons, which are electrically operated & at least one channel on Battery, but it's been many years since I worked on Challengers and I'm not sure what the latest CL604/605 version has.