“Are you sure you want to delete selected users?
ALL data in these user accounts will be lost, including emails, contacts, and any created documents shared with others.“
The best practice to retain the documents is to transfer ownership of the Google Docs before terminating the account. This can be done by designating a new owner from each document or for Editors and Viewers of the documents to make a copy of the documents in their own Google Docs repository.
The world of collaboration is powerful, yet when multiple stakeholders are involved, the logic needs to be appreciated.