If my physical body snuffs it but I suddenly discover my consciousness is still 'alive' and it meets a divine being - well I'll own up to God existing. Until then I'll probably remain agnostic.
Mind you, how will I know this being is God?
I struggle to think of any physical evidence that would persuade me (fulfilled prophecy, archeological finds etc.). It could happen but I've never heard of anything that comes even close up to now.
If an apparently all-powerful being appears in the sky one day and tells us it is God I'll be wondering about Arthur C. Clarke's dictum that "any sufficiently advanced technology is indistinguishable from magic".
Edited by MangyTiger, : Correct speeling of 'prophecy'
Never put off until tomorrow what you can put off until the day after