Can an employer terminate your visa or extension of stay in Thailand?

Connection is there. If you want to leave the country without re-entry permit, Immigration asks for letter of cancelling WP. That letter is dated, so easy to see the difference between day of cancellation and day of departure. If you leave on the last day and no questions are asked, yes you are lucky, but if you come back to Thailand and apply for new WP and Extension the dates will show up and you will have a big chance to be fined than.

Robert u are right, but but if he not cancel himself he is direct in overstay, so that's why I bring it to the point...because many think they can stay.....till the end of the extension .....many are lucky because the most employer don't cancel it at the Imigartion....till now there is no connection between the department of labor and the immigration....but sooner or later it will be direct online.

Not correct. The employer can kick you out and can cancel the Work Permit. But he has no influence on the stamps in your passport, that is your own responsibility. The day the contract stops and WP is cancelled the Extension of Stay based on working stops, you have to cancel that yourself at Immigration and can apply for a new Extension of Stay, if you do not meet any requirement you will get the stamp: Extension not approved and get 7 days to leave the country.