They could be surprised. Fanfiction often takes the characters in new and unexpected directions. So characters might be shocked to see versions of themselves or Captain America that are different from what they know.
They would probably be very concerned. They might first check his vital signs to make sure he's okay. If they find nothing physically wrong, they'd start to consider other possibilities like magic or mind - control.
Some of her terrestrial enemies, like certain power - hungry individuals or organizations, might see her true identity as a way to gain power. They could try to capture her and study her to replicate her powers. Or they could try to blackmail her into doing their bidding by threatening to expose her identity to the public in a way that would make her a pariah.
The Avengers originated in Marvel Comics. Marvel has developed a vast universe of characters and storylines, and the Avengers are a key part of it. Their adventures have been adapted into various forms of media, including movies and TV shows.
Captain Marvel is Carol Danvers. She gained her powers through an interaction with alien technology and has become a powerful hero in the Marvel universe.
Marvel justifies Marvel Comics 1000 by presenting it as a celebration of their rich history and a platform to introduce fresh and exciting story arcs. It could also be a strategic move to attract new readers and reignite the passion of long-time fans.