Quantum Mechanics after the detection of Gravitational Waves
No more than the observation of light waves disproves quantum mechanics.

Light has properties of both a particle and a wave. At low energies, the particle nature of light is hard to detect: radio waves are made of photons, but individual radio wave photons are pretty hard to detect. I'm not sure that we have directly detected individual photons with energies below the infrared band. 

Gravitational waves (probably) also have both a wave and a particle nature. The gravitational field is probably quantised. But at the frequencies and sensitivity at which LIGO operates, individual quanta cannot be measured. So this detection does not prove the ascendency of GR over QM.

If anything, understanding extreme events like black hole mergers might lead to a theoretical understanding of the quantum nature of gravity.