Remember the airframe is super cold after a long flight and holding. 6 degrees on the ground in those conditions would provide perfect conditions for ice accrual in flight IMHO.
Nope,irrelevant.
The only ice accretion due to long flight would be fuel frost on the top surface of the wing,very little if any performance issue.
The only reason of a stall would be,failure to engage AP while believing it was and not monitoring or reengaging the AP but not the AT, speed decaying after having manually reduced it to avoid flaps overspeed,or retracting flaps without a speed increase..possibly only using speed trend rather than actual speed.
In any case ,a stall warning gives enough time to react and perform the necessary maneuver unless of course both crews are tired,slow to respond and worse react in the opposite manner than necessary.
Very easy to fix the schedule issues,,,make it a legal requirement to limit change of circadian rythm each month...but hey that costs money ...