"Too hard to hit"? Who knows, maybe he's a sharpshooter or something?
As the movie is just opening here, I'd still wait about a week or so before making untagged spoilers.
That said... I don't necessarily think he's dead. It's the very definition of a "comic book death". Nick tells us the doctors called it and the Nick shows us the cards. Coulson wanted the team to come together. Nick used that. And we know (or think) Nick faked the cards. I was really expecting the final scene to show Coulson in witness protection or something.
Worry not, sharp-shooter or not, he is no match for the powers of the weather demon. With but a wave of my hand I could destroy him with ease. As for the rest, I do agree with your theory. However, they could easily have Phil's twin brother Will take his place in the next film-that would be epic.