While I never have killed my characters in my previous fanfics, I make them suffer, hence the angst, although it's not because I'm scared of the readers reactions that's why I never wrote character deaths. I'm not really scared of readers reactions, I can take bashing and criticism for my writing, it's just that I don't want to make a full-on death on a character without developing their characters and making the readers love and sympathize them. It would be too premature if you killed a character without making them feel loved or hated by the readers after all is what is my opinion. And, yes, death is realistic, since it happens in reality, but I though that, "Ahh...death in fiction is sometimes realistic, and sometimes not because of the plot itself", I have back up on that, I've read a lot of fanfictions swimming around on other forums and sites and believe me, some character deaths just feel awkward and rushed, it doesn't give that sense of "Oh...this is life, everyone dies..." because it hangs you up on the emotions...like, it isn't enough.
Death might be realistic in real life, but to make the readers feel and think of it in a realistic way is hard in fictions. If you can instill that subject of death in their minds, not just the word, but the meaning of death as a whole, then it would be a great eye-opener to people to value their lives and treasure each moments they have with people they love and cherish. But, since this is fiction, I doubt some would go out their way to actually hone something like that, I mean, it's simply for pure enjoyment...reading fictions and writing. People might complain that I'm talking all "novel-ish" so I'll just end it there.
On miraculous survival, I think that's also realistic, in a sense, the side of which humans want to happen, the hope of exiting despair and death, but why does miracles in fiction seem so unconvincing and realistic? Because of the portrayals of the miracles, it's simple just that. And also, if you kill your character for more than once and letting him survive through miracles each time, I think that would really be unrealistic and an overkill to the actual realistic feel of the plot, if ever that was the aim of course.