Can someone re-enter Thailand after exiting without canceling their work-related extension of stay?

Why don't you just obey the law and do things the right way?

You really should cancel both your work permit and your extension of stay before exiting the country. You'll be able to enter Thailand without issues but you will run into issues if you look for a long stay requiring interaction with immigration. Once they pick up on the fact you haven't cancelled your prior extension you won't get another until you cancel it (at the office where you got it, which can also fine you for overstay)