LOL. . .you're incorrect, in all respects.
Admittedly, the movies are (slightly) less explicit, but all the examples I gave are canon, and well documented, whether in comics or on screen. Don't know what your confusion is, here.
Re: Hawkeye "killing" Banner. . .don't wanna spoil the story for you, but Bruce survived the experience. See the current issues of the Hulk comic for how/why/what the current status is.
Of course, this is all predicated on the writers being consistent. Marvel doesn't have a great track record with this, so. . .there Is that.
I mean, to be fair, hardly anyone who dies in a comic stays dead, but the point is that if someone were to sneak up and decapitate Bruce Banner, that would effectively kill the Hulk.
As for Captain Marvel, I based my reply on the film, not any comics, and the film never spelled out how her powers worked, or if they were always active.
Let's be serious. . .Marvel will NEVER kill the Hulk. The reason shooting him in the head didn't work (it Should have) is because the creators decided so.
Equivalently, yes. . .cutting his head off (Bruce *or* Hulk) Should work, given the parameters of his power set, but rest assured: if it happened in the comics, they'd find a way to "explain" why it Didn't work.
I believe the term is "Plot Armor."
As for the film, I'm just commenting on (again) all that we can deduce from what they showed, on-screen. They could certainly come out and "explain" something different, but what we saw so far is what I pointed out, and the conclusions are pretty obvious.
Totally true. No matter how decisively any character dies, unless it's Uncle Ben or Gwen Stacy, they ain't dead.