There will be people that don't protect their coins and they will lose their bitcoins, but for those who are aware of the dangers and take the necessary precautions, they should have ample backups.  However, it is still possible for these individuals to meet an untimely end (hit by bus, stroke, heart attack, etc.) and have not yet set up plans to transfer their bitcoins to their heirs--or they may not have anyone to pass down their bitcoins to and in this case those bitcoins would be lost.