I propose we show a simple notification informing the user that the VR session has ended.  No interactivity required, and for whatever reason, it feels silly to tell users that they can take off their headsets (like we're giving them permission).

My recommendation: "The VR session has ended."

My full proposal here: https://docs.google.com/document/d/14UrWa5k4_7IPdFDowiaveduoGZIaGmrTbcpm4CsutuQ/edit#