Will Mumbai sink if a Tsunami occurs?

Any city runs the risk of sinking in the case of a tsunami. Mumbai as a city does not really have a great defense against tsunamis and any efforts to install them are tough due to the fact that Mumbai doesn't have natural coastlines and only a few areas have a natural mangrove forest. Although the probability of a tsunami is low, there are active earthquake regions around Mumbai that might trigger one.

Flooding of Mumbai after the tsunami is imminent and, for some time, it will stay flooded due to the fact that Mumbai soils are either sandy or loamy, both fairly capable of water retention. High rises will survive depending on how well their foundations hold out. Mumbai can never completely 'sink' by tsunamis but it can certainly be flooded by tsunami waters.

So, in actuality, the only thing that can sink Mumbai is the rising sea level.