Whether or not God exists, one must still choose how he is to live his life. That is to say, God does not function, as most would want him to, as guarantor of one’s actions. Good is good and bad is bad, regardless of whether or not God exists. Put in another way, wrong did not become right because God proclaimed it so. There was, of course, the alternative position raised by Christian existentialist Dostoevsky that if God does not exists, then all is permissible. I, however, sided with Nietzsche who argued that even if God did not exist, human artists could invent the good by which we were to abide.
I would argue, as I posted on his site, that there is also the alternative that good is built into the world because of G-d's relationship to it: that it is an aspect of nature like gravity, and that your belief or denial makes no difference for that reason. You can know nothing of Newton and still enjoy lobbing water ballons off a balcony, as I did when I was young.