Fat Gun and Tamaki weren't up against the decay wave. They were on the total other side of the country. Fat Gum and Tamaki were at the liberation army mansion and were part of the first group of heroes that fought Gigantomachia. What we saw consuming them was Gigantomachia's attack.
Oh darn, really? I completely got that mixed up then. Embarrassing. I did some reading up to see their last appearance and it was in chapter 280, where they appear along with the now dead Majestic and a couple others who are also dead now. Gang Orca's still alive though. Now I'm not so certain of their death anymore, they might be because others in that panel are now also dead, but if they're alive I'm also fine with it. I'll leave my Tamaki is dead prediction for what it is though, I'll get back to it when the current arc is over and I mark my predictions as 'came true' or not :P
By emotional support, I mean that they'd help cheer each other up basically. Its basically characters I think that would try and improve the morale of their students..
All of the students in 1A fulfill that role for each other right?
Of your predictions, Midoriya, Shoto and Bakugo have major roles to play for sure.
Ochaco I'm not so sure of, I see her remaining as a background character. People think she's gonna be Toga's foil, but I don't think so. Their meeting served to propel Toga's arc forward and to give Ochaco the realization that villains are people with feelings and emotions and they don't do bad things for the hell of it. However, I don't think she's gonna confront Midoriya with her feelings. I like that she decided to not let her feelings for him distract her, and instead let them inspire her to become a more capable person herself, to be the best she can be. I think that's great. Making her feelings for Midoriya become a main focus of her arc would be a waste of her character in my opinion. (not that you said it should become her focus, because you didn't, but, well, these are just some thoughts)
You said she could become a support character for the other classmates that were hit hardest emotionally by the war, but honestly I think Ochaco is one of those very classmates. Ochaco worked really hard rescuing people, witnessed heroes losing hope and quitting, saw all the death and destruction. The other students 'only' took on Machia and helped a bit at the mansion. That was tough, sure, and finding Midnight was really rough. But in my opinion it doesn't compare to what Ochaco and Tsuyu went through. Speaking of Tsuyu, we haven't seen any real focus on her, but considering her placid nature it's hard to imagine she was shook by what happened.
I like your thoughts for Tokoyami and Hawks.
I think Mina and Momo will get a bit more time spent on their struggles. Honestly, I think Mina might quit UA, and she might get a heart to heart talk with Kirishima before she leaves. It will be a nice parallel between them: at first Mina is the confident one and Kirishima is the insecure one, and now Mina has lost her confidence and Kirishima has found his. Perhaps Kirishima will inspire her to stay at UA, like Mina inspired him to become a hero when he was younger.
Momo, I'm not sure what kind of arc she'll get exactly. I think she will struggle with Midnight's and Majestic's deaths, who were both her mentors of sorts, but I don't think there'll be much emphasis on her and that she'll regain her confidence in her abilities, her place in the world, and find her role to play relatively quickly.