what if the craft is already in high altitude stall? in diving out of that stall how significant is the risk of overspeed and without ASI how to manage that risk?
I would have thought common sense airmanship would apply. You don't have to do a Stuka type dive to un-stall the wings. See:
https://en.wikipedia.org/wiki/Junkers_Ju_87
if there is a problem with all three ASI's and you have stalled it as well, then it is not your day
In that event, keep the nose slightly below the horizon for 30 seconds and keep out of buffet then very gently level out. Not forgetting to set cruise power as part of the un-stalling procedure. Count on losing at least 3000 ft in the recovery procedure. There is probably no QRH procedure for that combination of events so you simply have to `wing it`.