The question is why should any manufacturer be in f1? There has never been a successful manufacturer and so what if they are?
The destruction of the Renault team was caused because Briatore was thrown out of the sport. It became successful because it was Flavio's team and Renault got useful mileage, but now?
There is not a single reason why they should remain in f1. Formula 1 is a sport and the only reason people participate is because they want to. Just like any other.
And with the team now without its assets - Briatore and Alonso - its core value has been destroyed and it ought to be put out of its misery by the company because it is quite simply defunct.