I've been thinking overnight about your shift in focus for training to indoors from the risk point of view. As you said, it only takes one distracted motorist to change a life forever. But risk is a relative situation. For example, flying in a commercial aircraft is considered safe but compared to what. It is certainly safer than crossing a street on foot but is not entirely risk free, yet we do both. From my own experience, although I work to improve awareness of the situation around me, particularly when cycling, I know my attention span is distracted now and then. I know this because I have been surprised by some situations where if the motorist were equally distracted, that situation may have been dire for me.
Then to, it is not only motorists who present a risk. We can get into trouble on our own by being distracted and failing to either see or recognize in anticipation a developing situation. I've seen four cyclists go down, as JPPE recently did, in a situation that was likely preventable. In the end we accept a level of risk that has little to do with complete objective evaluation. I don't think we set a risk gauge to a particular level. Our best course to to continually evaluate that risk as time passes.