Business is business, and India does it with China way more than it used to do. And it would do more with the FSU and with China over airspace use were there to be a complete block of Iranian and Pakistani airspace when it comes to trying to continue service for flights to/from DEL and BOM whose routes most commonly have involved Iranian and/or Pakistani airspace use. Afghanistan is a landlocked country and the only way then in and out of it would be via the FSU, so cheap or not, it wouldn’t be much use except to waste fuel and time.

They would also shift more to going via or closer to some Arab countries too, but that doesn’t entirely preclude increased use of FSU and even Chinese airspace. Airspace shutdowns would mean paying up more, one way or another, for the airlines whose routes would be hit by a complete Iranian and Pakistani airspace closure.