One thing to make sure to do is balance any perceived risk to the real risk of being a couch potato. A sedentary life will kill you. If you look at the causes of death, death related to lack of excercise is way up there - cycling doesn't even get in the honorably mentioned.

It may be your luck to kiss a truck - but it also may be your luck to smeared by a falling plane, or zapped by a faulty electrical appliance. No one can tell you or your wife that cycling won't be the death of you. But anyone can tell you that lack of excercise will almost certainly do you in if something else doesn't get you before it does.

Go to the web and look up many of the common medicines that people take, often because they don't excercise. The potential side effects (which sometimes include death) do not deter people from taking them if they need them. Most people need to get regular excercise - and there are potential side effects. It is just the probability of you suffering them is low and you can reduce the potential for these side effects by riding sensibly and keeping your eyes open.