Junko has no real regrets that would make any sort of major difference to her personality, whether it's her actions or someone else's, so she'll more or less be the same as she's been.
Jolyne on the other hand has lots of regrets! But we'll stick to the death of her friend FF. Not her fault, but in this case, that won't have happened. Which means Jolyne's other friend would've died (since it was a one or the other type thing here) and her father never got his memory back (long story). And that really sucks. And would probably change some stuff later on, but the short of it is she'll be noticeably more bitter and withdrawn than she is normally. Sure, her friend's alive, but wow does everything that comes after that suck.
mostly just Jolyne for this one
Jolyne on the other hand has lots of regrets! But we'll stick to the death of her friend FF. Not her fault, but in this case, that won't have happened. Which means Jolyne's other friend would've died (since it was a one or the other type thing here) and her father never got his memory back (long story). And that really sucks. And would probably change some stuff later on, but the short of it is she'll be noticeably more bitter and withdrawn than she is normally. Sure, her friend's alive, but wow does everything that comes after that suck.