Only if you are HOPING that he will "die or leave" sooner, rather than later.
Just enjoy the time you have with him while he's around. There's nothing you can do about the inevitable parting. Everyone dies, and people are always leaving your company. So all you can do is enjoy their company while you can, and do your best to move on when they're gone.
Don't be silly. You're the most important person to him. He'll never leave you.
Assure him that you would never hurt him and he won't have reason to be scared of you.
Well, the only solution i can come up with is for him to learn to be brave. If he is facing troubles, he needs to be strong.
Sorry, can't think of anything else.
No. Cultivate the best relationship you can with your brother while you still can. He probably loves you more than you know.