If you haven't read Civil War II #1 yet, you'll be shocked to learn that the character who dies at the hands of Thanos is War Machine. This confrontation was teased in the Free Comic Book Day preview of the story, causing many readers to think it was misdirection, but it appears Marvel was unusually straight forward this time around. As for why Rhodey was the character Bendis chose to have Thanos kill, the writer stated, "
[Rhodey's] a very important part of Tony's life and he's a very important part of Carol's life. So they lose something of equal value but it means something different for the both of them. They both receive a personal loss based on the choice that was made. " What Bendis is referring to is the decades-long friendship between Tony and Rhodey and the recent romantic pairing of War Machine and Captain Marvel.
Bendis goes on to state that both Carol and Tony are hesitant to spark another conflict that divides the superhero community but it's ultimately Carol's decision to ignore Tony's advice and lead a preemptive raid on Thanos that pushes Tony over the edge. Learning of a tremendous atrocity that Thanos will commit some time in the future from a new Inhuman that possess prophetic sight, Captain Marvel decides to lead a team of Avengers to take down the Mad Titan before said event occurs. It was Tony's stance all along that they shouldn't make any rash actions based on things yet to happen and now he has to live with the fact that had he been more forceful, perhaps Rhodey would still be alive.
Rhodey and Carol began dating during Kelly Sue Deconnick's Captain Marvel run back in 2014.
Marvel's Civil War II will pit two factions - led by Captain Marvel and Iron Man at odds over the fate of an Inhuman that can predict crimes before they happen. Captain Marvel leads a group that wants to apprehend the criminals before they actually commit the crimes while Iron Man leads a group that's adamant that punishment can't occur before the crime is actually committed. Iron Man's stance is definitely softer than his position in the original Civil War conflict with Captain America where he wanted superheroes to register their secret identities with the US government. A Civil WAR II prologue of sorts will be made available on Free Comic Book Day on May 7th. Civil War II will ship on June 01. Brian Michael Bendis is the mastermind behind the event, while David Marquez is on art duty.