Zoe didn't sleep.
She wandered the ship. First to the kitchen, the lounge, the engine room. Sometimes Kaylee was there, asleep in her hammock, and then Zoe left quickly. Not so that she wouldn't wake Kaylee - a meteor storm wouldn't wake Kaylee, once she was out - but so that Zoe could retain her privacy. She needed to be alone.
She'd go down to the cargo bay next, but she never stayed there for long. For some reason Shepherd Book always came into her mind in the cargo bay - Book arriving on board, working out with Jayne, she and him trying to coax River out of the smugglers' hole after River'd seen Book with his hair down. Or up, as it turned out...She always felt a little pang in the cargo bay - surprise and grief that she'd never hear Book's near-sermons, his jokes, his laugh again.
And so somehow she always ended up sitting on the bridge. Not in his chair - never in his chair - but she'd sit in one of the other chairs, maybe, or on the floor. And she'd look at his chair, at his dinosaurs, out past the stars, while the tears streamed down her face - here where no one could see her, she could cry. She'd cry until nothing was left, until she could stare unthinking and unfeeling at the black void of space.
Mal watched her, silently. He knew his ship better than Zoe, better even than Kaylee. So he knew all the nooks and crannies, all the hiding places where he could watch unseen. He knew Zoe didn't sleep, knew how she stared for hours at nothing. There was a light had gone out in her soul.
He didn't talk to her about it. Didn't know what to say; couldn't think of a single word that would comfort her. She'd seen death before, just as he had. Lost friends before. But he'd never lost a lover. He couldn't tell her anything that she didn't already know, and now knew better and more deeply than he'd ever known. So he said nothing, and watched.
It was a month or two after the Reavers that he noticed something. Couldn't tell what, exactly. Zoe just moved more careful-like, sat different, and he couldn't figure out why at first. It was during one of those long nights on the bridge that he really saw. Zoe was sitting in the co-pilot's chair, but she wasn't looking out the window. She had a hand on her belly, and she was looking down at it, and smiling. Then she looked up, out at the stars, and Mal smiled as he saw the first hint of life come back into her eyes.