With Ben dead and no options left, the hour kicked off with Emily confessing to the murder of Victoria Grayson so she could be transferred to a higher security prison where bestie Nolan could plot her escape. Naturally, they had a breakout plan in place in case either of them happened to find themselves in jail again. Weak plot point? Sure. But this is Revenge, and they've gotten away with four seasons of such twists so now's probably not the time to break them all down. Could Jack, David and Nolan have proved Victoria was still alive with Emily behind bars? Certainly. But then we wouldn't have had the intrigue of whether she'd be the one to kill Victoria herself.
Of course none of that could have even begun to happen had Victoria not mistaken Louise's sympathy and loyalty for deranged madness. Would Louise have helped Margaux and Victoria carry out their death plot had she been privy to it from the start? Possibly. But a large part of that story relied on the character's blind faith to a mother she always wished she had. That involved putting Victoria up on a pedestal and believing that she was a victim in all of this. The moment Louise realized how involved her wannabe mamma was in trying to take down Emily (and how heavily she herself had been used), the tables turned and she realized Nolan and Emily had done more for her than Victoria ever would.
And that is why, by the end of the hour, Emily/Amanda was able to survive whereas Victoria was not. As was pointed out several times throughout the finale, Emily never killed for her mission; she only sought to ruin lives (because, sure, that's awful, but not awful enough). Victoria crossed that line when she killed Aidan last season in cold blood; there was never going to be any coming back from that. So adding in a cold-blooded assassin (Courtney Love, amusingly) for the final two episodes to continue carrying out Victoria's quest was in perfect alignment with her character.
It wasn't until Jack was mistakenly put into critical condition though that everything fell apart for the Grayson matriarch. Jack has always been the epitome of innocence on the series, so hurting him crossed that final line for everyone -- Margaux, Louise and even Emily, who switched from wanting to prove her own innocence to invoking her desire to kill. Fortunately for her her now-dying father intervened, bringing the themes of family and sacrifice full-circle just as Victoria reached up and shot Emily in the back.
Emily's death, in that fashion, would have been a truly poetic end to the story. But of course viewers have been following this journey for four years, and even when Emily did terrible things there was always a sense of wanting to root for her. To end it all at that moment would have been fine, but there would have been plenty of loyal viewers out there enraged that they didn't get to see the happily ever after between her and Jack. And has far as happy endings go, everyone left standing did well enough. Between Charlotte returning and standing by her sis on her big day, the toast saluting David Clarke and the rest of the dead characters from the past four years, Nolan's new mission of revenge and the final throwback -- a new puppy for Jack on the wedding day, everyone sailed into their own version of sunshine.
Now the only question that remains is whether Emily/Amanda actually received Victoria's heart, or if it really was all just a vivid dream.