Google Plus developers have a message for the managers of Google+ Pages.
If you remove a manager who has the ownership of a page, it would remove the page! So, make sure that the ownership is transferred to another manager before removing the manager.
Google Plus team said:
But, say you want to remove a managing account from your page. First, check whether that account is the page’s owner. If so, they’ll need to transfer ownership of the page to another manager before their account is removed from the page. Otherwise, the page will be deleted instead of transferred automatically to another manager.