The clock in the Burrow still kept an eye on him. The 'Percy' hand was set on 'work' a lot of the time. Molly used to watch it out of the corner of her eye, hoping beyond hope that it might swing around to 'home' again. She had spent a few long evenings looking at the clock and crying until Arthur came and took her to bed where she clung to him and tried not to think about Percy and how much she missed him, and how much she worried about him.
When his sweater came back at Christmas time that was really awful. It hadn't been much of a Christmas then. She tried valiantly to put on a bright cheery face for everyone else, and they all did their best to try to take her mind off of everything. But everything seemed to remind her. One less place setting at the table, one less face around the tree Christmas morning, granted it meant less grumbling, because Percy had been famous for being a bit of a grump at times, but he was part of her family and she missed the loss of him especially.
She managed. But she kept the sweater, wrapped up, in her closet, secretly hoping that he'd be back any day and she could give it back to him. She could imagine the scene in her head. He would come to the door and knock, and he would ask if he could come in. She would push the door open and hug him so tightly it'd almost crush him and she'd say that he was always welcome at home.
... but it had been a long time since Christmas now and it hadn't happened yet.
Molly kept the Christmas parcel safely tucked away and Arthur didn't say anything about it, despite his own fears that Percy wasn't going to come back to them the way Molly wanted him to.
Molly kept the things he'd left behind just in order, the way that he had kept them. But deep down she knew that none of these things would bring Percy home again, and that she was doing them because it made her feel good.
She had to keep thinking that Percy would come back home someday. It did no one any good to give in to despair. So Molly kept the sweater and kept her hope because it was all she could do.