I'm not going to teach you how geopolitics play in close door. But let me tell you this, no states want to close the door without exempting every possible scenarios first.
What do you think is going to happen in the next land border meeting between India-China and the Chinese argument that it can not accept the McMahon line because it was drawn by a colonial power?
With this greedy little stunt that you Chinese tried to pull, you have not only torpedoed your agreement with Bhutan to settle the disputes peacefully but also jeopardized the India-China agreement.
I mean now that China has publicly said that Doka La plateau belongs to China because British had signed an agreement and given it to the Tibetans, what ground does it have to still dispute the McMahon line?