Subterranean termites can live deep underground. They usually nest in the roots of buried tree stumps or some organic cellulose based material. Heavy rains at the surface level would do nothing to kill them. The only possible scenario is that a flood could wash away the soil in which they are living. This would have to be something catastrophic such as an avalanche or similar. Even then, it is possible they could survive. They are certainly one of Gods special creatures.