stellavision commented "I often wonder how Rand would have written the novel if she had a little bit of Robert Heinlein in her -- perhaps Dagny would have set up a home with all three men!" Heinlein's The Moon Is A Harsh Mistress, for example, features multiple-person marriages.
In most of her books
The heroine hooks
Up with two or three hotties
Who ravish her body.
So you can see how this Heinlein question comes up. You can see how one might make some guesses about her fantasy life.
In Atlas, she writes: "...she felt Francisco's presence through Rearden's mind, she felt as if she were surrendering to both men, to that which she had worshipped in both of them, that which they held in common, that essence of character which had made of her love for each an act of loyalty to both."
You might start to sense a trend
But at the novel's end
She's always down to one
Or, for poor Kira, none.
So whatever her fantasies, she doesn't think they're a good way to wrap up the story.
So if being polyamorous
Strikes you as highly glamorous
You may find the middle sizzles
But feel the finish fizzles.
In some of her public comments, she defended the possible morality of complicated "Design For Living" arrangements, but thought they presented difficulties, and still thought the ideal was one partner for life.
In her personal life
For a while she did have two men.
It ended in godawful strife
And she went back to one guy, again.
So the complicated arrangement in her own life didn't work out so well.
I know, I know,
Some will still say "Ho, Ho, Ho."
I'd say that by her own lights
She tried to do what was right.