In addition to the humanitarian nightmare and supply chain clusterfuck: how do you think dam failure will feed into geopolitics?
I would expect that China will almost immediately look to shift blame on an external foe in order to save face. US and India seem the most likely scapegoats. China officials have already tried to blame US for the WuFlu so it would be straightforward for them to extend that to TGD. And China's skirmish on the Indian border presents an equally convenient narrative of sabotage by a regional rival. This sounds like a recipe for whipping the Chinese into a war frenzy, a desperate attempt to maintain national unity.
Could also accelerate China's expansionism e.g. seizure of the South China Sea, Taiwan and Hong Kong, dam building and river redirection in the Himalayas to fuck over South Asia, etc.