Even before the script for Avengers: Endgame was written, directors Joe and Anthony Russo had some definitive ideas for what would be in the final film. And at a Q&A with Twitter HQ today, they discussed what some of those "cornerstones" were.
For one thing, they knew from the get-go that Cap would catch and carry Thor’s hammer, something the Marvel Cinematic Universe has been teasing since Avengers: Age of Ultron. Another cornerstone was that they knew that Tony would have to die.
“It was early in the writing process we started thinking about that moment ... in Ultron when Cap budges [Thor’s hammer] Mjölnir,” said Anthony Russo during the Q&A. “It’s just something that stays ingrained in your memory, and you want to find a way to move that idea forward.”
His brother Joe agreed, noting “there were a couple of cornerstones” like that when planning the story for Endgame.
"We made this movie, we knew [Captain America] was going to pick up the hammer. We knew he was going to say 'Avengers Assemble.' We knew that Tony was going to die at the end of the movie,” said Joe Russo. “Those were pretty clear from the very beginning."
And oh, yeah: time travel was also going to be a cornerstone of Endgame from the very start.
“We knew we were going to use time travel,” said Anthony.
Joe agreed. “That was another cornerstone.”
The interview was part of the We Love You 3000 Tour, Marvel Studio’s fan appreciation tour/victory lap being done to promote the film’s video release. (The discussion about the cornerstones of the script start around the 14-minute mark.)
At San Diego Comic-Con, Endgame screenwriters Christopher Markus and Stephen McFeely discussed with SYFY WIRE (see below) how the conclusions to Cap’s and Tony’s story arcs (which, in Tony’s case, was via death) were mapped out pretty well in advance.
By the way: in another recent interview, the Russos let it be known to those more obsessive fans that not all the Easter eggs within their movie have been found, so, keep hunting!