You can take your car all the way upto Khunjerab.
You can make through rough patches if youre careful. The car might scrape its underbelly a few times but thats ok. I dont know why Pakistanis are so worried of it.
As long as you dont damage/break anything a few scrapes to the underbelly are completely fine and have no detrimental effect on the car.
I say so because I have been scraping underbellies for a long time now.
But do check the current road conditions which might be bad due to construction of hydropower project.
This post is not to misguide you but to give an advice to make the best use out of your current circumstances.