Yes Hugh, I actually think you are right as the Indian guy who owns Force India is going to McLaren/Mercedes for his engines and drive train next year. It seems that he was never satisfied with the engines that Ferrari were giving him after he dumped the Spyker engines.
It is VERY true that Red Bull Renault have come on leaps and bounds in the last two seasons and now they are the fastest cars in the F1 circuit. Maybe that can happen to force India too, at least I hope so, for Paul Di-Resta's sake.