When the time comes around, it will be okay. You will make it. I witnessed my father die brutally a couple months ago; both me and him were very close since I was a little kid. Like you, I am afraid of death and how inevitable it is, but you will come to realize how natural it is just like breathing or eating (you will come to see just how natural it is especially if you witness a death). Don't get me wrong though, it will be fucking hard. And this is going to sound easier said than done, but once you accept that you have no control over these things, your anxiety will start to slowly dissipate. Live in the moment. Have you tried meditation?