if they weren't idols i think it would be: hcngjccng would have gone to music school to become a producer, i think his fling with fashion started later than when he was supposed to be choosing a major so idk, though i like this route better for fictional worlds
i always see seonghwa as having a more traditional job so MAYBE law, or maybe something related to media because he's always enjoyed creative fields it seems. he'd not be in stem i don't think
yunho would also go down a traditional role, maybe to stay in the family business but we don't know what that is so i'd say law or engineering
yeosang biochemistry or pharmacology i don't take criticism (just kidding i do but i think it works well for him). alternatively, psychology
san history or literature because i envision him as uni teacher or academic
mingi music production
wooyoung dance major
jongho maybe doctor?? idk... also something traditional

however idk if this is common knowledge 😭 they did go to college and are graduated and they all probably took something really boring like media or something else related to how to take care of massive amounts of money that they're garnering