When my niece's boyfriend, (19 years old), died of an undiagnosed heart condition, my 7-year-old son was devastated. He and Matt were great buddies, and he already considered Matt his "new cousin." He refused to be alone anywhere in our house, including his bedroom, because he was sure that Matt would visit him, as a ghost. He believed Matt wouldn't MEAN to scare him, but seeing any ghost would be scary. There was no talking him out of this because he felt that since Matt had loved him so much, he would be sure to try to visit him. It also turned out my boy had just read a supposed non-fiction book at school about the ghost of Abraham Lincoln haunting the White House. There was no arguing him out of his belief in ghosts, since he had read it in a "real book"!
No reward we could come up with for sleeping alone would dissuade him. Nothing was more powerful than his fear. I even tried convincing him that it would be wonderful to see Matt again, even as a ghost, because he was truly an incredible guy. Nothing worked.
So my husband and I let him sleep in our room, on a pile of sleeping bags and blankets on the floor. He called it his "nest." Sometimes he would nest in his big sister's room, which gave us a break...
This went on until he was 9, when we took in a foreign exchange student. The day she arrived, my son announced he was going to start sleeping in his room again, and he did! Male pride finally overcame fear, as he was now more worried about the student considering him a "baby" than he was about Matt's ghost.
Ok, not the most elegant solution, but it got him back in his own bed!