What happen if China stop sharing water with India

Any attempt of Diversion of water would be a huge damage to China for the following reasons.

Geography

1. This region is characterized by Active Earthquakes of 8+ Magnitude. Since the Indian Plate is colliding with Eurasian Plate. Also Himalayas are too young in Physical relief that they are growing at 8cm/Year in altitude.
2. There are many rivers that take their birth here and that is why it is called Water tower of Asia. These very young Rivers are flowing at fast velocity due to high gradient from the point of origin to their entry to plains, making V-Shaped valleys with steep gradient.
3. So what is the point with V-shaped valleys? These Young mountains with Gorges have soil that cannot be held very tight(No trees and roots to hold). These mountains are subjected to mudslides and landslides and the soil falls in the river path and obstructs natural flow.
4. Correlating point 1 & 2, Any attempt to obstruct the flow will be a massive disaster either naturally or man made. Just imagine a Nuclear explosion. This is because mudslide that obstruct water flow can hold certain quantity of water but if it is beyond the withstanding capacity, water bursts of through the fell soil and erodes the banks heavily resulting chain effect. Remember how Uttarakhand Flash Floods occured.
5. For any diversion of water to take place the basic thing is you need to construct a bund/dam across river and store water. The storage water will be diverted either through Lift, Canals, Making Tunnels.
6. Now which of the above three suits this terrain. Only Making Tunnels.
7. If we make tunnels in this terrain and when this area is frequently inhabited by earthquakes, the holding of soil in its place is further aggravated and chances that massive landslides and mudslides occurance is very high.
8. Attempt to store water for diversion will make water percolate easier than thought in these loose soils and boulders resulting in Endogenic rocks/soil adjustment leading to earthquakes which will be chain effect to the already earthquake prone area. The P-Waves and Surface waves( both Rayleigh wave – Wikipedia and Love wave – Wikipedia) in this region of Tibet will completely eradicate the existing Humans.
9. If Tibet has to think who is responsible for this? China will have to suffer.
10. Climate Change in the recent years further aggrandized the definition of disaster. Imagine if there is a cloud burst or Glacier melt. where will the sudden water be stored/diverted?

Geographically this terrain is not good for such experiments and any Indifference on this will be at the respective countries peril.

Here is the sample of mudslide for heavy rains from Google earth. Kindly look at how it cutoff the banks heavily. Now add Earthquake factor and Imagine for the same.