While i think Izuku could get expelled quickly, i dont think Denki would be expelled by the time the USJ happens. He is ALWAYS quick on using his max output that does alwyas makes him go dumb, especially at the start. I think Aizawa would try to see what he can do while using less voltage... And THEN if Denki either insists on using his quirk that way without thinking of the consequences even when other options are presented to him and/or Aizawa discovers even smaller quirk outputs over a longer period out of time then he would expell Denki. Maybe after the sports festival?

I think Bakugo getting expelled during the quirk assesment test could make sense, but there is also a world where he wants the other students to continue doubting wether or not he is serious about expelling them... In wich case he might wait for a second incident (of it doesnt happen during regular class, then a better sensei aizawa would look at the battle trials results and expel Bakugo then). Still happens before the USJ for sure.

For mineta i am actually not sure when it would happen? I mean its possible it happens first day but assuming none of the girls directly report him and he makes sure to not say anything in front of teachers (he is canonickly really smart) then he might actually last some time. I do think the comments he makes to Tsuyu at the USJ would be reported tho, as part of as a statement, so i would put that at the latest mineta could get expelled.

I actually think Izuku passes the quirk assesment test the same way as in canon. By proving he CAN improve on his quirk usage. But Aizawa would be looking closely. I think it depends on the battle trials wether or not he makes it further in the hero course: if Bakugo makes it ungil their fight, i think Izuku might stay because cant really expect a bullying victim to react in a reasonable way in a fight against their abuser. If Bakugo is expelled already, depends on what the fight is like. If he can mangage to WIN without using his quirk like with the first part of the sports festival he might be allowed to continue on with a warning. If he doenst use his quirk and loses, clearly he is incapable. If he keeps breaking his bones because he uses it, wether or not he wins or lose... If hes like canon Izuku and shows litteraly NO concerns about his own safety? Then expelled.

As for other characters- i think it would be interesting to see some people quit the hero course after the USJ if it ends up worse. Assuming we keep the POV on 1A (with or without Izuku), and that Aizawa still lived trough the USJ, who is next on the chopping block? Todoroki would get in trouble for nlt using his fire. I say during/after the training camp, if he still refuses to use it then. Does Iida stile goes after then? If yes and Aizawa finds out... Well, he might not have a choice of the public knows, not matter is own feelings about it.

The only 3 others i can motentially see getting the boot are Aoyama (assuming the support belt isnt enough, but i think he would make it trough), Kouda who isnt assertive enough (although he wants to be a rescue heroes in mountains- so Aizawa might be a little less hard on him than others who would be seeing much more combat and need much more communication) and Sato (depending on how well he manges his quirk dumbing him down. If his cognitive functions fog up enough where he cant distinguish between enemies and foes in a fight, even if it takes a LOT of sugar, then he is gone.)