Most people don't realize it, but "Goodbye" is an Old English contraction.
It literally means "God Bless Ye".
Of course, not everyone who says "Goodbye" knows, or cares about its etymology, but in this day of the ACLU, Michael Newdow's lawsuits and a group called the "Freedom From Religion Foundation squandering our courtroom time and resources, I can't help but wonder when this term will find its neck on the chopping block.
So, when an atheist says "goodbye" to us, maybe we should smile and say "Thank you, God bless you too". ;~D