I believe that I-140 need not be restarted again, and if the I-140 is retained by the employer he/she can still proceed with previous I-140. But the person will be considered as born in India and his/her PD will be charged as per India’s PD list.
Again the caveat is when filing I-485 or consular processing from Canada (you provide an explanation along with supplement J for the original I-140) that the person is now Canadian passport holder and job (I-140) is still bonafide with the actual employer.
I am adding a link from Murthy forum which clarifies that when a Indian person who becomes a Canadian, he will be charged as per Indian que for priority dates.
Again this is entirely likely but one would need to hire a experienced lawyer when that becomes a possibility.
Anyone with any other information, please let us know as well.
