Disclaimer: Not mine, yo.
She wakes up smiling, and he smiles back.
He's here. Vaughn's here, he's with her, and Sydney gets the feeling that she'll never be alone again. And yes, she knows that her life is still full of problems, even though SD-6 is gone; she knows she still has to deal with the fact that her mother is a terrorist in CIA custody, that Sloane is on the loose, that she can't leave the Agency no matter how much she wants to...
But she wakes up next to Vaughn almost every morning, and somehow life has never been better. And if that morning smile creeps back at odd times during the day...well, the world needs more happiness. And if she finds herself staring at him with a goofy love-struck expression...
At least he's staring back.
She wakes up smiling, and sometimes thinks she'll never stop.