[Warning for speculation and SPOILERS]
You've been warned! This is of course all speculation, but I think that the movies are actually going to stick to the comics for this one. Yup. That means...
We know from the Russos that even though most of the MCU ensemble is present for Civil War, these will absolutely be Captain America films. He's been set up as a character prone to incredible self-sacrifice, and I think this arc would translate very well to film. I will of course be very upset. But at least in the comics Cap comes back, so this isn't exactly permanent, right?
I don't think Rhodey will die; that trailer is probably misleading.
I don't think it'll be Spidey either; he'd be a good pick but the character is too new. They're not gonna pull another Pietro.
There's a slim chance for Natasha or Bucky- but Sebastian Stan's contract is pretty much a guarantee he'll be in a few more films so he'll probably step in as Cap. And Nat... I think the Russos just like her too much.