AOA
I have ridden to Khunjerab from Khi 3 times, twice this year.
My advice is NOT to even think of riding through Punjab on Bike during winter due to heavy Fog.
In Northern areas its suicidal to think of riding on bike due to fog and the likelihood of snow or rain which both spell DISASTER.
As a few ppl mentioned already, Babusar Top is now closed due to Snow and upcoming Glacier season.
Your best option is a safer drive by Car which can get you to Sost in upper Hunza. From there you can get updated information on Khunjerab to see if its open.