I would imagine that the cable itself contributes more to the headphone falling out than the weight of the headphone itself.
Also, I imagine you mean "likely lose just one of the pair", as losing one pair means losing both of them (not intended as a dig, just helping to clarify; your intentions seemed clear)
Also, I imagine you mean "likely lose just one of the pair", as losing one pair means losing both of them (not intended as a dig, just helping to clarify; your intentions seemed clear)