They don't dangle from a cable when falling like normal headphones or Bluetooth headphones that have a cable between each earpiece. Since it's also so comfortable, the user might not even notice they lost an earpiece immediately if they are not listening to anything. (which will specially happen if the user has incentives to use it day long).
And more annoyingly, you will most likely lose just one of the pair. Will you be able to buy just one eapiece and pair it alongside the old pairless earpiece? I don't think so...
edit: fixed wording as eric_h pointed out