It would be pretty bad for them lol and the thing about retconning your own story doesn't work like I said mc can be in love say it back actually meaning it to Dessie, clearly loves Kosuke if you romance her and also can choose a love option with mina when a more lust like option is present so for them it is pretty serious mina gets very sad even if you say you cannot be with her and this is after you slept with her the second time because she thinks she found love, this was her before MC's agreement,now imagine she left the temple and came to live with you lol openly breaking up her vows if you tell her you are going to be with her so imagine now saying no lol.
Atleast for mina it will be really bad for Kosuke as well it will be hell and for Dessie she will not show much but she will be pretty depressed.
Like i said it would still make sense to give this option to break up tho I can't help but wonder about the sh*t show that will happen with Mina you already had chance to break it with mina after sleeping with her the second time and mc instead chose he wants to be with her and then she deadass just came to live with you so yeah that one isn't going to end well at all she would be humiliated the man she left her vows for and place for the man who told her he will be with her now just threw her away.
Me personally I will do a solo Eldra run and then a Eldra with sides run if the option to break it with others gets added i might do the third run to see the **** show that happens because of this.