Please first of all send a note to RTO also that you have sold the vehicle as such you may be saved to a little bit from any future damages for negligence done by person you sold vehicle.
Secondly it is your duty to ensure that vehicle is transferred to that person and law is clear on that point. If your advocate has suggested you to get matter settled in court better to get it done the court may refer it to lok adalath and once it issues a direction to buyer to register vehicle in his name you will be protected. There is nothing to worry these issues get solved within three to six months or even earlier.