Would a dual flame-out in a 737 at higher altitudes leave you with enough windmill hydraulic pressure to fly the plane? After you (the Captain) quickly decide who must fly, does the other guy put on his oxygen mask and then start the APU using just ram air, as stated on the red-bordered Emer. checklist?
By the way, a (M) Douglas DC-9 or MD-80 needs no hydraulics to fly, for any primary flight controls.