Honestly there is no WHAT IFS because they were GOING to
1. The Cheating was going to be exposed no matter HOW SNEAKY Miyuki was, that's why it was a SHOCKER that Ms. Aono find out for her. Note she outted herself because Ms. Aono was IN the dark and all she had was she saw her around a boy she didn't know. IT was Eiji's state in CH1 when he came home, him hanging around Ai and Miyuki's CRYING about him "snitching" that confirmed the truth to her! Just not the WHOLE TRUTH as she told her, for the SAKE of her friendship to the little bitch's mother and their PAST relationship, she was giving her the CHANCE to slick back into the shadows in which she came without ANY MORE then her GLARE and contempt (Something she would LATER regret to herself when she FINALLY got to see what happened in CH 1 to her son and what Miyuki allowed to happen at school once Eiji told her about the bullying, well more she found out from the TEACHER as the two together got the Recording of the incident that started all this! Yeah turns out Miyuki is STILL BLIND to the public as a FOODIE Streamer had been nearby, her the commotion cause Kondo is a loud idiot, and recorded the whole scene! While you couldn't hear what was going on, it VERY MUCH showed Eiji never grabbed her on her wrist BUT KONDO DID that caused the bruising! All this is what leads to Ms. Aono's lawsuit and police filing on her son's behalf that leads to Kondo's Juvie, well partially as his actions when the cops came to him made it SO MUCH WORSE for him! And the lawsuit at Miyuki! While Kondo was the start of the slander that lead to Eiji being targeted, Miyuki is EQUALLY responsible as she allowed the picture to be taken, and she HAD her chance to confess, but said nothing, allowing the slander to go forward unresisted! Lying for Kondo only ASSURED she is an Accomplice now, even if she PLEADED Kondo said he'd never use the Photo for anything other then scaring Eiji off, that will just be seen as an excuse she used to avoid responsibility and her part. ESPECIALLY when she was given a chance to ..To add
1A (The "To Add"): Tachibana (the name of Eiji's Senior and the President of his Club and the MASTERMIND who send Kondo to Miyuki in the first place) was ALWAYS going to have it exposed, the slander was a STROKE of a opportunity! But Eiji was ALWAYS going to find out because it was about emasculating him so he couldn't focus on his Novel. This situation allowed her to "LEGIT" remove him from the club, AND if not for his Kouhai, would have TRASHED his novel when "getting rid of his stuff" So NO she was NEVER going to be able to hide the relationship.
1B (Miyuki's logic): Her logic behind her hiding this shit was that Kondo was a Senior (same as Tachibana and Endou since they were on their last year before they graduate to University) so her plan was to have her CHEATING relationship with Kondo, and once he graduated, she'd "never see him again" (just like SO MANY fools! Assuming they'll never see a problem again because they left the area! Till they are DEAD you are forced to deal with them no matter what to be honest) but as said with "1" and "1A" that was ALWAYS doomed because she was A TOOL, a Means to an End for Tachibana and a TOY for Kondo! But remember she did it to herself, she KNOWS cheating was wrong, hell her FATHER'S abandonment of her and her mother which of course involved Cheating should have shown her as her mother tried hard to hide it the effects! But she still did it ANYWAY because she was thinking she was sneaky and thought she could have it all! And as they say "Those who want to have their Cake and Eat it to, will get NEITHER!" Even if you take out Tachibana, Kondo WOULD have made her do to Eiji what he got Eri to do to Endou, and he DID as shown in Chapter 1! It's why Miyuki's only WINNING option would have been to NEVER TAKE KONDO'S PROPOSITION TO BEGIN WITH! She doomed herself the second she said yes and fucked him! and Doomed herself further by FAILING to return all of Eiji's goodwill over 10 fucking years when it was her turn out of pure self-preservation! In the end she is alone....because she MADE herself alone!
2. Miyuki WOULD have commited suicide, there is no BUTS to that! Seeing how once she DID find out about his suicide attempt, what he went through and finally getting to "talk to him" only to be REJECTED by him for the obvious reasons that she CONTINUES to disgrace the girl in his memories and finally realized he never HATED her, he was INDIFFERENT! She almost offed herself in the same fashion he had tried to do! And like that, it was Ai's intervention that prevented it! In Miyuki's case "calling her OUT for still being a coward and aimming to HURT Eiji more because INDIFFERENT IS NOT HATE and she KNOWS as Ai knows her death would only DESTROY Eiji further! If Eiji HAD killed himself (or failed and only BADLY crippled and injured himself instead! Either all), it would have destroyed Miyuki, even if she held on, the guilt would have been WORSE, and worse for her! Tachibana has no more reason to keep the charade going, So Kondo would be FREE to "do with her as he pleases" and remember, his end goal was to "enjoy her" till he got bored then abandon her just like he did to Eri cause he got OFF on her realizing she had been made a FOOL of, and her PLEADING not to be abandoned since she CRASHED her life trying to satisfy him! Take note this would have IMMEDIATLY caused Ms. Aono to find out what was going on SOONER, the school would have IMMEDIATLY done what their doing now only alot more FIRM (And I doubt Miyuki would do what she did HERE in that "What If" since she would have the FULL understanding his "suicide" WAS her fault and that guilt WOULD make it hard to even TRY to lie! And of course we can't forget the GOAT of the story himself
2A (The GOAT) You really think Endou would have remained quiet! He was ALREADY aimming to destroy Kondo and his "supporters" the second the slander and pariah on Eiji Aono happened! You think he won't go EXTREME then he already was doing the second he discovered Eiji's Suicide attempt/Success! And this would have been BAD for him since he COULD be saved in this universe, but in the other universe, there would be no Eiji to calm him down or stop him from going BALLASTIC on ALL INVOLVED.