One of the features in Google hangouts ensures that no record of your chat history is stored. To enable this, you simply have to go to −
Hangouts> Open any conversation> Go to Setting> check for the option 'Conversation History'> Uncheck the box placed in front of this option>
Now the answer to your another question on retrieving the messages is that 'You, as a user' cannot retrieve; however, your employer, in case you use a shared network, can not only see but retrieve even from 'off' mode. Although, I know that Gmail claims that no one can see and retrieve the history from this mode, but that's just a claim, not reality.