I know it's kind of late to be discussing this, but could Doflamingo's power actually save him?
There was a theory that Law saved him, or Doffy used Law to save himself, but I think there's a much simpler explanation: Doflamingo's power can do something like the Bara Bara fruit. He can simply reattach his head with his own string powers. He'll still be alive right after his head comes off (death by decapitation is not instant. You are just completely helpless when your head comes off), but DD isn't helpless because he can control strings with his mind. As BS as that sounds, and unfair as it implies, I don't think Oda cares about common sense or fairness when it comes to DF powers. What matters is that DD is beatable. And he can be defeated, just not with common reasoning.
However, I will admit my previous explanation is boring, unoriginal, unimaginative. I would like to think that the body we see is a perfect fake replica, and DD controls it perfectly, even putting Haki into it to seem even more real. I can totally imagine that Doflamingo is hiding somewhere, completely avoiding detection by clever use of his powers, but controlling the stage masterfully. The only way to detect him is by having great Observation Haki. I'll also admit that he won't use his fake body all the time, especially if there is no where to hide.
And while I like my second theory, he's being served food and watching the gladiators. He would need his actual body to eat, so having a double eating your food is dumb.
So that's my 2 theories, imperfect but fun to think about. Maybe Law does want DD alive for right now, but I wouldn't make a bet on it.
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