If the Dark One was around.....

[Thalia]

Mwahahaha! Interesting question.

Soren would for sure end up Forsaken, as a trade off for knowledge. No cost too high.

Oriena would also probably end up on the "dark side", just by her associations and general attitude.

I think the rest would stay with the Light. Though having said that, Thalia could probably go either way, depending on what people she surrounded herself with.

Well, I was wrong about Soren. He's light-fearing. Who'd a thunk it.

Ori, probably still dark side, though I think she'd need incentive. She wouldn't do it for the sake of it.

Thalia ended up Black Ajah in her 3rd Age life. But generally she's a "light" person, it does just depend on her influences.

Did I really only have 3 characters back then?! (edit: oh, nevermind, I said "the rest")

Asha - light
Eidolon - light, for sure
Zeke - well... (darkfriend with delusions of grandeur)
Helena - she's for the light, though you wouldn't know it. Her soul is all about balance so I suppose under the right circumstances.
Morven - could probably go either way. Sekmet was SCARY
Natalie - light, obviously, though she can make very morally grey decisions. 
Nhysa - hmm, you know I'm not sure
Noemi - probably light. Though if Hades had a 3rd Age life, whatever he was
Raffe - he was for the light
Sesuna - light
Sofia - Forsaken material
Tenzin - light
Vena - light
Visha - dark most like, depending on if she was persecuted. Or maybe she'd be unlucky and born shadowspawn 0_o
Zhenya - light