Never make the mistake of underestimate just how shit thew quality life can get in a communist country and still be combat capable.
To the best of my knowledge, the Chinese are aware of the risk the 3 Gorges Dam poses.Never underestimate how much your Army and Air Force gets gutted when a few million Gallons of water bulldozes your bases.
They've probably already moved the vast majority of its military formations and installations out of the flood path.
If anything happens, the dam collapse will wipe out a big chunk of China's population and it's most well developed industrial region, but I don't think its military capability is going to be impacted.