If you remove a user from your Company plan, what happens to their projects?
When a user is removed from your plan, anyone who has been added to the project as a collaborator will still have access. This is dependant on the project owner keeping you as a collaborator on a project.
To keep access to projects for a user you're about to remove from the Company plan, you should make a copy of that user's project before you remove them from your plan. Find out how to do this here.