Gatsby has lost Daisy by the end of chapter seven in The Great Gatsby. The issue is decided by then.
It's actually decided earlier in the chapter, when Daisy says to Gatsby: "...you want too much!" She continues:
"I love you now--isn't that enough? I can't help what's past." She began to sob helplessly. "I did love him once--but I loved you too."
But that isn't enough. Gatsby's illusion is that he and Daisy have a special love, a love that transcends the norm. For Gatsby's illusion to be complete, he needs Daisy to have always loved him (since their relationship five years earlier). He needs her to have married Tom only for money, rather than for love. And Daisy won't lie and say this is so.
Interestingly, even if Daisy were to later change her mind and choose Gatsby, Gatsby's dream would remain shattered. For the relationship to be equal to his illusion of it, Daisy has to have always loved him and him only. And that, Daisy insists, was not the case.
Tom knows he's won when he tells Daisy to go ahead and ride home with Gatsby, because, he says,
He [Gatsby] won't annoy you. I think he realizes that his presumptuous little flirtation is over."
Nick knows, and Daisy knows, too. Gatsby probably knows, also, although he still refuses to give up.
It's important to note that Daisy's choice is not about money--Gatsby has plenty of money, and he certainly leads a more exciting life than Tom. He has the nicer shirts, remember, and he's the one who throws the great parties.