I really do believe Lauren somehow gets the identity of Sidney, and vice-versa, maybe Sid being kidnapped by Sark, CIA can't tech up such an initiative because they don't have cloning technology + Lauren isn't jailed within their building + We know from spoiler that Lauren takes a big risk to infiltrate the building. Also Sark is a big fan of cloning process, he did it to his previous gf, and can tell Lauren about the process, promising her that she could regain her old face later (evil Francy couldn't because the data was lost in servers datacenter wreackup). Real Lauren masked as Sid then goes to CIA HQ, gets documents she needs and sets the place on chaos.
Then Vaughn gets his hands on Lauren aka Sid right after the rampage (maybe he finds her on satellite feed near covenant base or whatever) and tortures her, then realizes from cellphone call - like Dixon telling him "Sidney" just destroyed the office - she's the "wrong" person.
I believe Sidney' choice about "her two loved ones" will be she'll just have to go help Nadia/Daddy and leave Vaughn alone, then he'll commit suicide because he won't be able to face the idea he did torture Sidney by mistake and she'd never forget it.
About the Sloane/Nadia part I have no idea. I don't think both will work together in s4, maybe Katia will kidnap her and protect her like she was supposed to, until Irina returns. Now that Sloane has found her daughter and probably the ultimate Rambaldi secret, I don't see him going back to the bright side ever, maybe he'll choose to have Rambaldi spirit resurrected into his body (that's what he would really die for, considering his madness about Rambaldi's life) or something and will even forget about Nadia's existence because memory brainwashed.
Then Vaughn gets his hands on Lauren aka Sid right after the rampage (maybe he finds her on satellite feed near covenant base or whatever) and tortures her, then realizes from cellphone call - like Dixon telling him "Sidney" just destroyed the office - she's the "wrong" person.
I believe Sidney' choice about "her two loved ones" will be she'll just have to go help Nadia/Daddy and leave Vaughn alone, then he'll commit suicide because he won't be able to face the idea he did torture Sidney by mistake and she'd never forget it.
About the Sloane/Nadia part I have no idea. I don't think both will work together in s4, maybe Katia will kidnap her and protect her like she was supposed to, until Irina returns. Now that Sloane has found her daughter and probably the ultimate Rambaldi secret, I don't see him going back to the bright side ever, maybe he'll choose to have Rambaldi spirit resurrected into his body (that's what he would really die for, considering his madness about Rambaldi's life) or something and will even forget about Nadia's existence because memory brainwashed.