Old_Geezer - "Who is to say that existence is not viable unless you are human ? Surely the idea is that humanity is related to your present existence and you leave that behind. Non-existence need not be the default condition, and more than nothing the default universe (for want of a better term)."
I apologise in advance if I'm misinterpreting your post - I find your wording a little confusing. I admit that may be my failing.
However, if I concentrate on, "... Surely the idea is that humanity is related to your present existence and you leave that behind..." then my previous assertion still stands. If you leave your corporeal body behind and exist outside of it, then unless you take with you all of the aspects of you that make you "you" then how can it be said that "you" go to heaven (or hell, or anywhere else)?
Let me try and make my thoughts clear. You, I and every other human being on this planet are made up of a complex mix of kindness, anger, jealousy, empathy, hatred, love, sorrow, joy, etc. If just one of those multifaceted emotions is removed from your psyche then you are not "you" any more. You're a different "you". If all the so called negative emotions were removed from you, then you would cease to be you. You'd look the same and sound the same but you wouldn't be "you" in any meaningful sense.
As for, "... Non-existence need not be the default condition...", well it is if one is attempting to be rational. It's the null hypothesis. That you cease to exist when you die is the most logical explanation and the one with least question marks attached to it. You didn't exist before you were born and you will cease to exist when you die. The "heaven" hypothesis which inevitably leads to the "supreme deity creator" hypothesis is not logical, requires great leaps of imagination to support and is ultimately narcissistic in nature.
In words of Monty Python, "We come from nothing, we are going back to nothing. In the end what have we lost? Nothing!"