Does the book Atonement tell the reader what happens to Robbie and Cee after they leave Briony at the station?

Yes, but it's buried deep in the epilogue. In the movie, Briony is being interviewed as a famous writer near the end of her career/life. In the book, Briony is being feted at a family birthday party at her former home, which has since been turned into a bed-and-breakfast inn. Ironically, the misbegotten play she tried to put on at the beginning of the book is finally put on by her grand-neices and nephews during her party. Her brother attends in a wheelchair, as he is very old and feeble. She is looking back on her life, and she reveals what happened to Robbie and Cee -- but it's said more in ping, than in a long, drawn-out explanation. It's really no more than a sentence or two. Sorta leaves the reader shocked and saddened that there was no "resolution", but in a way, that was the whole point -- for some things, there is no atonement or resolution. The characters didn't have one -- why should the reader? :-)