To me, the question of whether MC should be in a relationship with Mina is a separate question from whether she should be with Ian. The Edwin x Mina question is dependent on the Ian x Mina question (unless we're talking about a poly relationship
), but whether we like Edwin with Mina or not doesn't change the fact that it doesn't seem like Ian and Mina are a good fit.
Sure, Ian can be rehabilitated into a good man. He's got a lot of good traits and he's young enough to grow out of his bad habits. I don't think it's a short path to loving himself enough to not continue to be a womanizer or a relationship self-saboteur, especially in his current occupations. Mina's got her own issues with confidence and self-image, not to mention that her mother poorly modeled romantic relationships.
However long it would take for Ian to become "boyfriend material" and for Mina to figure out who she wants to be, I doubt the relationship is salvageable. Yea, they were a cute couple, but I didn't get the "true love" vibes from them. It takes more than being cute together to get over betrayal. They don't have a previously solid, long-term relationship that can help them pull through the tough times of rebuilding the trust. Even if the relationship can be put back together, is that kind of baggage going to make for a happy, healthy relationship? Is the relationship worth her effort to have to put their history out of mind and pretend that she's not constantly worried that he'll do the same thing again? Is Ian a strong enough man to humbly and calmly reassure her when she breaks down over her doubts about him?
Letting these two guide each other from pseudo-adulthood into true adulthood is a recipe for a breakup in three-and-a-half years with two very poisoned hearts. My cost-benefit analysis of the risks versus rewards of reestablishing the relationship puts the expected returns too low to justify the expenditure. They should cut their losses and become better people for their next relationships.
Clearly I'm biased, projecting my own real world experience onto TD's imaginings, but this is how I like to look at realistic plots like this. If the question is whether TD can put these two "back together" long enough so we can see another double date scene, sure it'd be completely believable. Plenty of people hurt each other, break up, get back together, then rinse and repeat for years, but I'm not sure that reading another version of a scene we've already witnessed is worth the disappointment I'd feel in watching the MC let his friends do that shit to each other. I think we all know that several of the plot lines in PC are zero-sum, so I'm looking for as many realistic happy endings as possible.