The 13th principle is the dead will be brought back to life. How will the dead be brought back to life if those whose bodies were completely destroyed in a battle or plane crash ?
The Revival of the Dead will obviously be miraculous, and Jewish tradition teaches that even the sick, old or "destroyed" will also be healed. Tradition teaches that there is a bone called the "Luz" which always survives, and from that the dead will be revived (sounds something like cloning, but we'll see how it will be done when the time comes, for it actually may be fulfilled via medical developments which are also Godly revealed!).