A penny dropped from any height will not even break the skin, let alone kill someone. This was busted on MythBusters. "Firing a penny at terminal velocity (65 miles per hour (105 km/h)) into concrete and asphalt disks and a ballistics gel head with a human skull failed to result in any penetrations, likely because the speed is too low and a penny's mass too small. Even when fired from a rifle, the penny was unable to penetrate concrete or a ballistic gel dummy's skull. Even modifying a rifle to shoot a penny at supersonic speeds failed to cause a penetration."
In another example, a guy dropped pennies from a weather balloon and allowed them to hit him..they bounced off. http://abcnews.go.com/2020/story?id=3131332&p...
Your story about the gum creating a dent in a car also isn't plausible. If this were the case, every hail storm we have around here (in which the stones are roughly the size of chewed balls of gum) would result in widespread damage, which doesn't happen.