Depends where y'all mountain bike........I worry more in the backcountry, not about life, more about Bears, Cougars, and other unfriendly wild creatures.
Had two Bear encounters while biking in my day, very scarry. Been attacked by an Owl (thank goodness for helmets) Rode on trails that had Cougar warnings, those I fear the most, sneaky buggers. It's a good feeling to hit the parking lot some days after trail rides.