You can enable Chat | History so that users can store conversation logs in their Gmail accounts so that they can review them later, if needed:

Google Hangouts allows users to find and talk with anyone outside the organization who has a Google account. In Sharing options, you can choose whether external users can see a member's status to see whether they are available. It's recommended to enable the option to warn users when having a Hangout outside the organization:

Administrators can make it so that Chat invitations between members of the domain are accepted automatically: