Under no circumstances will China ever intervene directly in an Indo-Pak war, much less for a highway.
Generally Pakistani's tend to keep peddling these among numerous other fantasy flights to feel more secure.
Genesis, please take a look at what your own journals and think tanks have said and the history of Chinese actions.
Then look at the topography, whether even if China intervenes directly, would it have an impact in the time period that is required to make India go from offense to defence.
Now ask the question again and you will get your own answer.