What happens to your I140 approval if one moves to canada from a different employer
I far as I know its between you and your employer. The employer has the option to revoke it.
I think once its approved and employee stays with the employer for 6 months after approval, Employer can not revoke it anymore, only he can withdraw it, which retains your priority date.
But what i am looking for here is, if one moves to Canada after that, since for india the I485 is not concurrent, it would take another 10 years for it to be concurrent, in that scenario can one come back to US, if yes how and on what visa?
In that timeframe you could possibly have Canadian citizenship. You could just get another H1B or use the TN visa. Also if you are working for a company that has a US presence then you can just use an L1 visa.