God and Existence are not clearly defined.
Existence is just an overloaded term: Existence for a teapot is different than existence for a song, that is different from existence for a book character, that is different from existence for a mathematical proof, etc
The experience of human existence has also never been scientifically proven and therefore this argument is useless to this debate. We do not understand the brain function or the cognitive sequencing that instantiates our experience of life or the afterlife.
The attributes of God were clearly defined in the parameters of this discussion. No other attributes are relevant to this discussion.