India wants more the transfert of western technology for their domestical programs than not having just russian stuff. But the fact is that they are not mature to develope their own things and westerns are not going to give them their best technology for low prices. That's what happened with Dassault, they wanted a factory for the rafale, rafales, ToT, meteors ... for very low prices that's why at the end they went for just 36 Rafales. The final contract has nothing to do with what they wanted.
This the same with Grigorovitch frigates. They localy produce their own Shivalik class frigate which are bigger and "improved" Talwar class and have the project 17A frigates. But they stil ordered 6 Russian Grigorovitch. The prices are almost the same but they chosed Russian frigate, maybe their is a reason.
For maintaining the Mig-31 and Mig-29 SMT, they can just give this work to Sukhoi or Yak with all the technical data transferted to them. And they ordered 30 Aircraft as of today, not 180. I don't really know if their was a contract signed, the plane is still tested by the air force. The hole thing was communication and marketing. But if they order them, well I agree Mig will be saved.