Captain America could be initially shocked but then determined to help. He might try to talk to Tony about his own experiences of loss and how he found the strength to keep going. He'd probably encourage Tony to see that he's not alone in his struggles.
Pepper might be completely devastated. She could be by his side constantly, trying to bring him back to a better mental state. She might use her love for him and remind him of all the good he has done and all the people who still need him.
One possible reason could be the extreme guilt he feels over the consequences of his inventions. In many stories, his tech has been misused, causing destruction and loss of lives. He might feel like he's responsible for all the chaos and that there's no way to fix it, leading to a suicide attempt.
Abby would be all over Tony, bringing him some of her special energy drinks (even though they might not be the best for a sick person). She'd also use her skills to try and find out what's wrong with him in a more scientific way. Ducky would of course offer his medical expertise, and might even tell some long - winded stories while examining Tony to try and keep his spirits up.
Steve Rogers would probably be deeply disappointed. He values loyalty highly, and Tony's betrayal would shatter the trust they had. He would try to find out the reasons behind it and might even try to bring Tony back to the right path if he thought there was a chance.
Some of them might be disappointed. Captain America, for instance, might feel that they've lost a great asset. But at the same time, he might also see it as an opportunity for the Avengers to be more independent from Stark's sometimes self - centered ways. Thor would probably be a bit confused as he was used to Stark's quick - witted remarks during battles.
It's often portrayed as a cry for help. Tim might be shown as feeling isolated and alone, and the attempt is his way of reaching out in a very extreme way.
Harley Quinn might get really into it. She has a wild and unpredictable personality. She could start to role - play some of the scenarios from the fanfiction in real life, much to the confusion or amusement of the other Squad members. It would be in - character for her to embrace this strange new view of their world.
He would probably be overprotective at first. Tony has been through a lot, and the idea of his daughter having mutant powers, which could make her a target, would be scary for him. He might try to keep her locked away in the Stark Tower, but that would likely lead to her rebelling.
The Avengers would be in a state of panic and fury. Captain America would likely lead the charge to find Tony. He'd use his military strategy skills to plan a rescue mission. Thor might use his godly powers to track down any signs of Tony's whereabouts. Black Widow and Hawkeye would be on the lookout for any Hydra agents or informants. Hulk could be a wildcard. He might be uncontrollably angry and ready to smash anything in his path to get to Tony.
He'd probably be shocked at first. Tony is always so caught up in his own world that a secret daughter would be a huge surprise. But then he'd likely be protective. He might try to keep her away from his dangerous life at first, but as he gets to know her, he'd start to include her in things.
Natasha would probably be very supportive. She's seen their relationship develop over time and would be happy for them. She might also be the one to help smooth out any bumps in the road during the wedding preparations.