What is the significance of Daisy's question about what they will do with the rest of their lives?
Daisy's question about what they will do with the rest of their lives underlines the pathetic and ominous implications of the Buchanans' combination of vast wealth, limited intellect, and restless boredom. Tom, Daisy's husband, is particularly discontented:
I had no sight into Daisy’s heart, but I felt that Tom would drift on forever seeking, a little wistfully, for the dramatic turbulence of some irrecoverable football game. (Chapter 1)
Moreover, we already know from Tom's declarations that he is dabbling in ideas that are far more dangerous than a little recreational adultery:
“Civilization’s going to pieces,” broke out Tom violently. “I’ve gotten to be a terrible pessimist about things. Have you read ‘The Rise of the Colored Empires’ by this man Goddard?”
“Why, no,” I answered, rather surprised by his tone.
“Well, it’s a fine book, and everybody ought to read it. The idea is if we don’t look out the white race will be—will be utterly submerged. It’s all scientific stuff; it’s been proved.”
“Tom’s getting very profound,” said Daisy....
“Well, these books are all scientific,” insisted Tom, glancing at her impatiently. “This fellow has worked out the whole thing. It’s up to us, who are the dominant race, to watch out or these other races will have control of things.”
“We’ve got to beat them down,” whispered Daisy, winking ferociously toward the fervent sun. (Chapter 1)
Tom is stupid, paranoid, energetic, and vastly rich, and he indifferent to the damage he does others in pursuing his will. This all adds up to great danger.
One of the key ironies of the book, of course, is that it will be a cunningly camoflaged white member of the "lower orders" who will try to steal Tom's wife away from him. But we can confidently predict that this experience will make him no less racist, no less paranoid, and with historical hindsight, no less dangerous than he was before his encounter with Gatsby:
I couldn’t forgive him or like him, but I saw that what he had done was, to him, entirely justified. It was all very careless and confused. They were careless people, Tom and Daisy—they smashed up things and creatures and then retreated back into their money or their vast carelessness, or whatever it was that kept them together, and let other people clean up the mess they had made. . . . (Chapter 9)