Well - to the best of our info - vehicle number portability is not much encouraged in RTO - due to negligible requests and old data maintenance issues for it. Its not much in demands - but - if someone desire - yes - it seems likely possible to transfer registration number from an old car to new car

Before having car registration number portability - First step is for Cancellation of Registration of Old Car
Section 55 of Motor Vehicle Act deals with cancellation of car registration - As per it
>> If a motor vehicle has been destroyed or
>> has been rendered permanently :- incapable of use,
then only the vehicle registration will be treated as cancelled

So - if the old vehicle is scrapped, you may approach RTO with original RC, photographs along with insurance claim records / dealer certification for cancellation. Also - you can place a request that the same registration number is requested for your new car

Guess it wont be so easy in RTO too to cancel registration - as they may also ask for record / documented proof that no challan / criminal case on vehicle is pending. You may also be required to get NOC from Traffic Police for No Dues and Civil Police also that no criminal offence on car.

RTO Office will cancel the registration providing no taxes, fines pending and they are satisfied that vehicle is destroyed or became incapable of use.

Once registration is cancelled, you can simultaneously apply for re-registration with old number - for that you have keep rto officer in loop.

Source