I have witnessed two people die during bike races, but they were pedestrians walking in front of 1) the finishing sprint in Fitchburg around 1979, and 2) the peloton in the middle of nowhere north of Concord, NH, around 1981. The first was an elderly man crossing the street "to get an ice cream". The second was a truck driver carrying a bag of groceries, looking down. He was between the break and the peloton, so the lead police car had already gone by.
I did know two women who died (many years apart) in bike races in New England, but I wasn't present. One was hit by a car in Stowe, another hit an exposed curbstone with her head in Arlington, I think.
But while these are rare things, the number of crashes per low-category event probably approaches 1.0. In terms of the likelihood of being in a crash before you get out of Cat5 (which is no guarantee of safety), you are almost certain to be involved in at least one. I don't think there is anything approaching the danger="risk of injury" of bike racing that people regularly sign up and pay for. But the number of broken bones and such is actually pretty low; so the danger="risk of severe trauma" is low, but anyone who has been around awhile knows someone who paid a big price.