You say that suicide is murder and since the suicidal person is dead they can't be forgiven for that sin. As a person suffering from major depression, and having had suicidal thoughts and attempts I would like to say that when one attempts suicide they are not in their normal state of mind. If they are not then how can they be judged by God for something they obviously have little or no mental control over. I would equate suicidal thoughts to a state of mind similar to a mentally handicapped person since you must obviously be mentally handicapped in some respect to consider suicide at all. Haven't you said the mentally handicapped are not responsible for their sins? If so then by that same token neither are people that commit suicide. If there is a place we go after death, before we go to heaven, then wouldn't it be possible to be forgiven for our suicidal sins (or other sins) there instead of here on Earth? Also doesn't the Bible mention that the gap between life and death is too great for man to cross? Seems I read this somewhere but I can't recall. If that saying is in the Bible then wouldn't that preclude ghosts and other such things people say they have seen or heard or felt from being real? I know Jesus raised Lazarus from the dead but He obviously doesn't have the limits we as humans have in crossing the gap of life and death.
You are right in saying that I said suicide is murder that can not be repented of. As I pointed out in my answer, that is my view, but there is no direct scripture to say what happens to a suicide after he dies.
Not intending to belittle your condition, or anyone with thoughts of suicide, I must point out that your argument has been used in relation to any murder. There are those who would try to say that no murderer should be punished because nobody in their right mind would consider murdering anyone. Therefore, any murderer must be out of his mind and should not be subject to punishment by man or God. Obviously, since many scriptures say that murderers will be punished (Numbers 35:16-19; Romans 1:29-32; Revelation 21:8), God doesn't buy that argument. It is an argument that takes all responsibility from one who has the ability to make a choice. Unlike the retarded who can not always understand right or wrong (and there are some retarded people I know who can tell the difference), even many of those with suicidal thoughts know that suicide is wrong, but choose it as preferable over other options. Many, I am told, never intend to complete the act, but are not prevented in time. God will judge the intent of their heart.
You ask, if there is a place between life and judgement, then wouldn't it be possible to be forgiven there? The Roman Catholic Church holds (without scriptural basis) that there is such a place, called purgatory, and that those who are not the worst of the worst can work off their sins there. Matthew 25 indicates that we will be judged for what we do on this earth, not on anything that happens after we die. Then there is the passage you mention, Luke 16:19-31. Jesus indicates to a man who died, but while there were still people alive on earth, that he could not cross over from where he was to heaven. He was where he was because of what he did on earth, and could not change his eternal destiny.
You are also right in saying that such a gulf would preclude ghosts (manifestations of dead people) being seen on earth under normal circumstances. When Saul had the witch of Endor call up Samuel's ghost (1 Samuel 28:7-14), this was a shock to her because for once this was real and not something she had faked. After Jesus was raised from the dead, many came out of their graves and walked around Jerusalem (Matthew 27:52-53). These were clearly exceptions, and not the normal way things happened.
Thank you for your astute observations and questions.