I think what's more important is not whether Vaughn pops the question (which I do think he will), it's whether Sydney would say yes - what do you think?
new thought - maybe irina became head of the covenant in order to ensure Sydney's survival? That's how lauren knows about the lock box because if jack faked Irina's death - and irina was head of covenant - then lauren could have found out that intel somehow. Or irina and/or jack leaked it to...
I also just can't see irina being the cause of all of Sydney's pain - it just doesn't make sense. If it were true that Irina was behind sydney's kidnapping, allison's death, etc. then I think she'd be more evil than sloane - which is an interesting thought.
It still doesn't make sense to me...