Kintsugi (http://brightly-lit.livejournal.com/42343.html) by brightly_lit focuses a little more on the reunion than dealing with the grief, but it's amazing and I hope you'll read it anyway.

http://dayspring.skeeter63.org/goldhome.html

It's a little different from what you're looking for but you should check out http://soserendipity.livejournal.com/9576.html (http://soserendipity.livejournal.com/9576.html)
Summary: “Dad’s on a hunting trip and he hasn’t been home in a few days.” Sound familiar? Sure, except this time, 18-year-old Dean confronts Bobby with the news. Because Sam? Sammy was taken when he was six – vanished off the face of the earth – and despite Dean’s best efforts, they've never been able to find him. John thinks Sam might be dead, but Dean can’t bring himself to give up hope that maybe, one day, he’ll have Sammy back at his side.

The Missing Piece https://www.fanfiction.net/s/4892061/1/The-Missing-Piece Summery: Teens! Sam and Dean didn't grow up together. Sam's neglected in foster care and paralyzed. Dean's a troubled teen hunter. They meet at school and become best friends. Dean realizes that Sam is the missing piece that can bring his family together