Re: Before asking if God exists one must define God.
Apparently "God" is that ineffable being to whom those who believe in him credit all responsibility for that which Man does not understand.
Therefore "God" exists in the minds of some men, and when the last believing man dies, God dies with him.
If we notice, the "Gods" of the Maya, Inca, etc., have suffered that fate. They no longer exist because no one believes any more.
At least we now have some limits on "God". Much like the Higgs boson, we may not have captured it but we are cornering it.