If Death God claims your life, don't you die? I'm not so sure there's any difference whatsoever. Even more so because Oro didn't live the rest of his bizarre life armless, only until he possessed another poor sod. So, rather than being held captive, his arms died due to being devoured by Death God. If the jutsu meant eternal imprisonment in a separate place, Minato could have sealed Kyuubi wholly with it, freeing the world entirely from its presence. But apparently that would have merely meant killing Kyuubi and thus only ensuring it reappears randomly later.