The majority of the governments of Earth decided that the greatest threat to humanity was the proliferation of super powerful individuals. To that end all enhanced, magical, mutant, alien, and artificial individuals were exiled from Earth. It didn't matter where they went as long as they were gone. Any that didn't leave were hunted down and dumped into a dimension were time doesn't exist leaving the individual to go mad in an endless ever-present now.
Old Man Whitman
Stripped of his Ebony blade Dane Whitman could have given up being the Black Knight and remained on Earth. However he chose to return to the Ultraverse where he could continue fighting to protect those in need. He was summoned back by Stark to lead the last Avengers team members in a quest to prevent the hunting down and execution of the last remaining humans in the universe.
Old Man Parker
Spider-Man chose exile in the Spiderverse. After years spend fighting villains and training new generations of Spider-Heroes he returned to his own universe expecting humanity to have come to its senses. What he found was the remnants of the Earth and moon and Humanity dispersed to the stars.
Old Man Banner
With Earth's destruction Banner lost the will to continue the struggle between himself and the Hulk. Hulk took full control but it was a hollow victory. Without the internal struggle to fuel his rage Hulk has been reduced in size and strength of a normal human he doesn't even have Banners intelligence instead he only has his green invulnerable skin.
Unlike other humans that were allowed to remain on Earth as long as they turned in their enhancing technology Tony Stark wasn't given a choice. He was imprisoned and forced to spend the rest of his life creating weapons to guarantee that super powered individuals never returned. An irony that wasn't lost on Stark, and like when he built the prototype Iron Man armor he worked in secret to procure his freedom. Using Vision's body as his starting point Tony was eventually able to upload his consciousness into the synthetic form. Donning the symbiot derived armor STARK kept Tony's skull and favorite suit jacket, just to stay fashionable, he now finds himself fighting to save a species that he is no longer a member of.
The son of a Wakandan scientist Horus was already on track for a bright future. Then Earth was destroyed. The Egyptian God gifted him with flight and the ability to see everything. Horus then modified an old confiscated Black Panther suit for his own needs and has joined the Last Avengers in place of the Black Panther.
With the destruction of Earth the Guardians of the Galaxy found their time being dominated by human centric problems. The team was stretched thin and at Rocket's suggestion the Galactic Avengers team was formed. Truth be told Quill suspects that the real reason was that Rocket was sick of the crap from Pete Junior.
The Daughter of the mutant Wiccan and Skrull/Kree Hybrid Hulkling, Captain Marvel retains her parent's shape shifting, super strength, and magical abilities while gaining mutant abilities of super speed and magnetism. She actually leads the Galactic Avengers even though Major Victory insists that he is the true leader.
Peter Quill Junior spent most of his youth sneaking out to hear stories about his parent's exploits as members of the Guardians and the X-Men rather than learning to fulfill his role as a galactic leader. Eventually he stole a starship and tracked down the legendary shield of Captain America. Donning a costume of his own design he tried to join the Guardians for a time before Rocket convinced him to join the Galactic Avengers.
When the mutants were exiled Storm found herself in the realm of Asgard once again. Sick of the infighting amongst the mutant factions she settled and eventually found true love. Eventually giving birth to twins Woden and Brigid. Woden, ended up Asgardian but with no special powers until All-father Thor game him a re-forged mjolnir that turned him into the current God of Tunder.
Born a mutant, Brigid had the ability to bend the elements to her will. while quite powerful in her own right she leaves the control of the weather to her brother often only control of air in order to fly. Instead Brigid prefers to forge and empower metals spending as much of her free time as possible in the lands of the dwarves learning their unique arts.
Wilber completely human, however he does take after his father, The Prowler, and does his best to keep up with the others on the team with whatever bit of technology he can get his hands on. Though his costume my look simple it is actually a kinetic energy diffracting techno-mail that protects him from any form of non-energy based weapons. His headset is linked to his brain and imparts enhanced senses. He also equips Spider-Mans classic web shooters rather than more lethal weapons as a tribute to his father.