Death is the end

Sorry if I have misunderstood. Are you saying one should not appreciate life or cannot properly appreciate life if they know death is the end? I really do not get this logic. We all live and we die, that is the cycle of nature. If someone knows beyond doubt death is the end why would that stop them from appreciating life right now? Would they not go out and achieve more in life? If someone knows death is the end sure some might be depressed about it, but others will appreciate it more. 
 
Also you talk about positive scenarios. Is disease positive? Just because something is natural does not mean it has to be positive. Nature does not work this way. The belief system here by proponents seems to be that one can not appreciate life if death is the end, and what is the point in appreciating anything if we die? This I do not understand. There has to be an afterlife for you to appreciate anything in life here now? Makes no sense to me! 

It also seems you invent a 'meaning' in your life if an afterlife exists. Also makes no sense to me! It seems belief in an afterlife comes with a lot of philosophical baggage.

With regards to your first paragraph, I addressed this already. Some might appreciate it more, my guess without a doubt is that the vast majority of people would not. This is exactly my point - you do not understand the implications of this scenario. What is the point of "achieving more in life"? There is no point. Your progress or achievements are devoid of any real meaningfulness, because nothing is this scenario "means" anything. It just "is", and then it "is not". Your contention that this situation would in some way make people appreciate life more generally is what I disagree with; not in premise, which is logically sound. But there's more to life than logic, and I am confident that most people would not feel that way at all.

For your second paragraph: I didn't say the word natural, and have no idea what your point about disease is. I think you have a fundamental lack of comprehension about the implications of this scenario, and that's clear. What is the foundation for meaning in the situation put forth in the op? "Create your own meaning" is a platitude people like to say, that has, ironically, little meaning itself in a universe in which there is nothing to life. Note that you took what I and others have said and twisted it entirely: I never said you have to have an afterlife to have meaning. Hypothetically, let's say that a God exists who is interested in the collective evolution of his creation, but there is no afterlife. In this situation, were we aware of it, at least we are serving some purpose. That doesn't involve an afterlife, but it involves a purpose from which people can at least draw meaning. There is a humongous spectrum of things from which a person can ascribe meaning that don't fit into a neat little personal afterlife. On the flip side, there is no value in "appreciation" because there is no value in anything in the proposed situation. Perhaps the absurd and impossible to comprehend-ness of this is what is making it difficult for anyone to understand, which certainly makes sense to me. So what you've done here is try to set up a caricature of what people here have said that isn't at all representative of their views. No one has said "There has to be an afterlife for you to appreciate anything in life here now!" What we have said, is that if death is final and there is nothing else, and we are a cosmic accident and nothing more, etc. etc., it's pretty much impossible to ascertain some meaning or value from that if you're being intellectually honest.

With regards to your last sentence, you don't "invent" meaning. I think the best way of putting it is that you "find" meaning, with the key being that meaning is actually rooted in some legitimate purposiveness as opposed to false creations out of the atoms and subatomic particles bouncing around randomly in your brain. You're just making assertions with no supporting statements with that entire last paragraph... I think, again, that you are just ignoring the immense philosophical baggage that comes with your scenario, as laid out by most of the people who have responded here.