In my opinion, it should be assessed based on a case-by-case basis. Generally, I think the former owner should remain in the Company for a certain period of time to ensure the transfer of knowledge and experience to the new team. This is also to prevent the resignation of the existing employees in view of the change of operating culture and the owner. In many cases, the employees left the Company once the owner left due to personal reasons such as the feeling of insecurity or uncertainty of their career prospect.
