Avengers: Endgame set up the future of the MCU in the most complex way possible. Spider-Man: Far From Home revealed that the Multiverse will now be in play, and we saw in Avengers: Endgame that alternate timeline(s) were created. The first permanent change in the timeline happened when Loki took the Tesseract, and the last happened when Captain America went back to the past to live the life that he never could.
But another major change that happened was the coming of Nebula, Gamora and Thanos to the future. Loki and Cap still have the time to go back and erase everything, but Thanos does not, since he is dead! Moreover, Gamora from 2014 now stands in 2023. This version of Gamora never met the Guardians, so in this alternate timeline, the Guardians of the Galaxy may never be formed. In this timeline, the events will become totally different, so if Vol. 1 becomes so different, how can be expect Guardians of the Galaxy Vol. 2 to be the same.
Throughout the MCU, only 3 big villains have been threats to the entire Universe apart from Thanos. Dormammu, Hela, and Ego the Living Planet. Now, Hela and Dormammu will be handled, but Ego may actually go on to become the Universal big bad in this timeline, and there’s nothing that anyone could actually do about it.
Reddit user Ljgor has pointed out the fact that with the Alternate Timeline not having Thanos and his army left, Ego the Living Planet becomes the one that kills the entire Universe in his course of the Expansion. Here’s what he wrote:
“In Guardians 2, Ego’s plan is to kill everybody living in the universe, leaving only him. However, the Guardians stop him from doing this. Later, in Endgame, Nebula from 2014 brings Thanos and Gamora from 2014 into 2023. This would theoretically create a branch timeline in which the Guardians never exist. The Avengers would probably be busy with Hydra at the time, having no idea about Ego. This means the Ego there is a timeline where Ego killed everyone.”
No one actually knew of the seeds that Ego planted for his Expansion. With the Guardians not having been formed, Ego could have probably got hold of Peter Quill, and with Peter not having Gamora by his side or his team, he could have teamed up with his father. Together the two could have killed everyone in the Universe, so this sort of becomes an MCU plot hole if the branches created by Loki, Captain America, and Gamora’s absence are in the same alternate timeline.
If these three time changing events create different branches altogether, then there are 3 different timelines, apart from the one where the Avengers win. In this case, there’s one timeline with Loki’s Mischief. Then there’s one where Captain America gets old & then there’s the one where Ego kills everyone in 2014.
If all these three events happen in the same branched timeline, then the only way Captain America could grow as old as he did was if he got rid of the Super Soldier Serum from his body and became his original self. This allowed him to grow old faster and then he met Sam in the original Timeline before Ego killed everyone. But that probably didn’t happen, so let’s just believe that all three events happened in different branches (although that doesn’t make a lot of sense), and Cap returned to the original timeline from his branch. This way his return does make sense and it doesn’t give me a headache! Damn Ego can create a massive plot hole!
Avengers: Endgame stars Robert Downey Jr. as Iron Man, Chris Evans as Captain America, Mark Ruffalo as Bruce Banner, Chris Hemsworth as Thor, Scarlett Johansson as Black Widow, Jeremy Renner as Hawkeye, Brie Larson as Captain Marvel, Paul Rudd as Ant-Man, Don Cheadle as War Machine, Karen Gillan as Nebula, Danai Gurira as Okoye, Chris Pratt as Star-Lord, Zoe Saldana as Gamora, Vin Diesel as Groot, Dave Bautista as Drax, Bradley Cooper as Rocket, Gwyneth Paltrow Pepper Potts, Jon Favreau as Happy Hogan, Benedict Wong as Wong, Tessa Thompson as Valkyrie, Samuel L. Jackson as Nick Fury, Cobie Smulders as Maria Hill, William Hurt as General Ross, Tilda Swinton as Ancient One and Josh Brolin as Thanos.