People who ask silly questions, deserve silly answers. But I will be grown up.
If a person truly, knowing what he is doing, commits his life to Jesus Christ for Him to save him, yes his salvation is secure for eternity. He can say 'I have been saved once for all' (Titus 3.4-7). Your problem is that you think you must save yourself with a bit of help from God. It is CHRIST Who is the Saviour, NOT US. If such a person was not finally saved it would mean that The Saviour had failed in His job.
I would never say that your backsliding did not matter. But everyone backslides to some extent. That is why we need a Saviour Who saves. He says of those who go astray, 'I will seek them until I find them' (Luke 15.4). He will never let those who are truly His sheep perish or be destroyed (John 10.27-28).
Your final scenario is just ridiculous. Someone whom Christ has truly saved would not behave like that unless it was because his brain had been so badly affected that he did not know what he was doing. Do you think God would punish someone who went astray because they were insane and unable to control their own actions and behaviour? He would look at them in terms of what they were when they were of right mind. And His saving work would not have failed.
Your problem is that you overlook the POWER and LOVE of the Saviour. We are not masters of our own destiny. GOD is master of our destiny.