My grandfather was said to have died screaming that he would not go. I'm not sure what was the status of his salvation at the time of his death from leukemia. It was disturbing to the family to say the least. I HAVE heard of it. I don't believe it was demons because "a bad tree cannot bear good fruit." I think people struggle with their final moments regardless of salvation. I watched my uncle pass saying he was scared over and over. He died of scirrhosis of the liver. When physical life is so overwhelming, it is understandable that the end will be a difficult transition into spiritual life. It is hard for anyone to let go..dare I say, men/providers/protectors especially. Maybe he is talking to God, others have argued with God, and still maintained ther salvation. Maybe God is giving him the opportunity to come to terms with the idea of physical death before it actually occurs. This could be a blessing for him, easing the struggle of passing. A gift from God. I know it's hard for friends and family, but maybe it is making leaving easier for your dear friend.