They could have had (or started) the APU and then restarted the engines. IIRC from testing, there is some time before HYD 1 & 2 are depleted (depends on useage of course) and HYD3 is powered by electric pumps. A Challenger or CRJ are best thought of as a FBW aircraft with one channel being pre-stressed Bowden cable! The CF34 does not have sufficient core flow when windmilling to provide ancilliaries but the older Lycoming-powered CL600 I was reliably informed provided sufficient flow to supply hydraulics right to touchdown.
Many years ago I did some work looking at installing a G Load recording system for a Flight Inspection Challenger. The loads routinely experienced at low altitude produce the equivalent of multiple flight hours in airframe life but the Challenger just shrugs them off so I shudder to think what the loads must have been for it to be a writeoff - double figures?
Last edited by ICT_SLB; 10th Mar 2017 at 04:30.
Reason: Added windmilling comment