Go forward with the case probably a G D is registered and the FIR is not taken,
A, G D report is enough for the claim but i would suggest you to push the officials to take an FIR and to take a case against the Driver who drove the bus,
As the bus was hit from behind your car the driver who drove the bus is the culprit,
And as soon as it reaches the court the culprit as per the FIR have to pay a minimum of 2000k as a penalty.
And this has to be paid from the culprit's pocket which i am sure that the Govt would not pay for the driver.
If all such cases are registered and the Bus drivers have to pay such penalties, then i think such careless drivers will be more careful in the future.
The insurance company's advocate will be appearing for you at the court so there will be no headache for you in the future in this case, so please go ahead.