If the employer moves to another province and the employee as well at any time before he gets his PR, he can no longer get PR under that PNP. You would have to sponsor him under the PNP of your new province. If the employer moves but the employee stays, he may have issues with the PNP if they find that he no longer has a job offer / sponsoring employer in his province depending on which provincial immigration class he is applying under.
A PNP applicant must intend to settle in his PNP province when he applies under PNP as well as when he lands. Anything else would be considered misrepresentation. However, moving out of the province after getting the PR is allowed.
If you are considering moving the employee with you, keep in mind that if he is on a closed work permit, it will not only specify your company but also your location. If the company moves, you should actually get him a new LMO and a new work permit in the new province. However, if he is on an open permit, then it's not a problem.