@metalhead
Duplicate file can be acquired but let me warn you beforehand that the process is not going to be easy. When i lost my file,i was informed about the procedure which starts from putting a news first in the newspaper, then filing a report with the police station,going to the company to get a copy of original invoice so on and so forth.
An easier way would be to arrange some CHAI PAANI or pull some strings at excise & taxation office.
Whether selling a vehicle without its file is an issue or not, i don't know but when i was selling my bike without file, owner backed out at the last minute due to unavailability of file.