Yes, I would.. but I'd be pretty surprised if that were the truth, so surprised that my criteria for trusting the source would be extremely high.. it's hard to imagine how someone could impress me enough or provide enough evidence to prove there is no God to me.
Also, I take issue with the implication that there is an absolute, objective fact as to whether God exists or not. Profound truths about the universe are a 'slippery' thing with respect to their being assimilated by our puny minds and binary-truth-valued semantics. Whether there's a God or not probably, at worst, depends on 'how you look at' the universe. And by that I don't mean trivially that 'whatever you believe, is true for you' as some people like to claim, I mean that a lot is lost in translation between truth and ideology or even ideation.
Mystical or cosmic truths are just too holistic, nuanced, complex, subtle, interconnected and multidimensional to be readily amenable to rational analysis and assimilation. So it's kind of that what's true (or what semantical statement should be considered 'true') depends on what aspect of the cosmos you're focusing on or 'highlighting,' what your outlook is, how you regard the terms of the question, etc. Niels Bohr (famous physicist) even said, 'The opposite of a fact is falsehood, but the opposite of one profound truth may very well be another profound truth.'
This is why mysticism seems so hard to grasp and may even seem anti-intellectual or just illogical, and why many mystical teachers, all of whom may be very wise individually, seem to say so many contradictory things (another reason being, of course, that humans are often wrong and fallible--even the genius and enlightened ones).