If I have deployed using my user id, and when you left company your ID will be deactivated. What happens to your objects which you have deployed to the target environment.

Typically process model will stop working or have issues with nodes configured to run in the context of the model owner.

Always use a technical account for any deployment to upper environments.

Hi, when any user leave the organization. The objects modified by them will still be visible. If the process model is modified as run as whoever started the process model then it will break.

This case probably occurs in the Dev region and the process models needs to republished with Deploy admin account. 

For higher regions this issue will not occur as they are already with deploy admin account.