As nice as it is to ride with others, even with highly experienced former or current racers and non-racers, the risk of leaving some of your epidermis on the pavement, or worse, is always present. It's actually one reason I don't get too bent out of shape by riding solo about 50% of my rides. Mistakes, or a moment's inattention that causes a crash can happen to anyone who happens to be a human - sad but true.
Also, a "group" could be just one other riding partner as far as being taken out by another rider. As stated by others here, the odds of being taken out increase the more there are in the group.
So many risks we all take by just riding a bike.