At the time of Harry Potter and the Chamber of Secrets we have 2 conscious and functioning Horcruxes - young Tom Riddle from the Diary and the "main piece" hiding somewhere in Albania.
Young Tom Riddle reveals that he is not aware of the future - it's Ginny who told him that Voldemort was defeated when trying to kill Harry.
“Well, you see, Ginny told me all about you, Harry,” said Riddle. “Your whole fascinating history.“ His eyes roved over the lightning scar on Harry’s forehead, and their expression grew hungrier. “I knew I must find out more about you, talk to you, meet you if I could. So I decided to show you my famous capture of that great oaf, Hagrid, to gain your trust—”
“Haven’t I already told you,” said Riddle quietly, “that killing Mudbloods doesn’t matter to me anymore? For many months now, my new target has been—you.”
“So I made Ginny write her own farewell on the wall and come down here to wait. She struggled and cried and became very boring. But there isn’t much life left in her… She put too much into the diary, into me. Enough to let me leave its pages at last… I have been waiting for you to appear since we arrived here. I knew you’d come. I have many questions for you, Harry Potter.”
“Like what?” Harry spat, fists still clenched.
“Well,” said Riddle, smiling pleasantly, “how is it that you a skinny boy with no extraordinary magical talent—managed to defeat the greatest wizard of all time? How did you escape with nothing but a scar, while Lord Voldemort’s powers were destroyed?” There was an odd red gleam in his hungry eyes now.
— Harry Potter and the Chamber of Secrets, chapter 17, The Heir of Slytherin
It is quite clear, that the Diary only has a memory of 16 years old Tom Riddle.
If he were to win that fight and consume Ginny, what would happen with his memory? What would be his memory state at the moment?
This question addresses whether there would be 2 Voldemorts and how would they interact. For the sake of this question, I set that aside and actually ask in what state exactly will Voldemort's memory be and why. I see three possible outcomes:
- The memory of Tom Riddle from the diary will merge with the original Voldemort's memory (though I'm not sure in this one since Voldemort doesn't seem to have any connection to his Horcruxes as he doesn't even notice them being destroyed)
- Riddle's 16 y.o. identity will dominate and be more or less single source of memory since that is Horcrux's condition
- vice versa original Voldemort's identity will prevail since he's the original one and have higher ground on this. He can't die while there's at least a single Horcrux, while Horcruxes can be destroyed, which places his original part higher.