Would it matter to who? Would it matter to me? Maybe, but it depends. If we presuppose the existence of a God, and we presuppose that this entails that we have an afterlife. Then, yes, it probably would matter. But this brings us back to your original point, that morality exists on account of God. If, however, you blow us all up and there is no afterlife, whence we are all reduced to cosmic dust, I want to say that it won't matter. Not unless somewhere in the universe there exists some other intelligent being who can judge our actions according to their moral standards, which at this point we are considering moral standards to be inventions of culture. Even then, though, since their standards are as subjective as ours were, it wouldn't really matter; it wouldn't be either a moral or an immoral action, because such a distinction simply doesn't exist.

It seems that you want to conclude that since we do have morals that God does exist, but that isn't a necessity. As I said before, there are ways to explain our morality through some kind of social evolution and game theory (this is Skyrms main view, and he supports it with evidence and reason and so forth...It is convincing, but only to the point that most sound arguments are. As it is, I don't want to draw any conclusions about the objectivie or subjective quality of morality).

In my previous post I wasn't as clear as I wanted to be on some of the problems that arise from making this relation between God and morality. I don't think I can be as clear as I want to at this point, either. The best I can do is point you towards the theory that got me thinking about it in the first place: Theistic Voluntarism. You will find it in any philosophical dictionary, as well as some interesting points made by Descartes and Plato (see Euthyphro).

This discussion is already getting way out of control in the forum, so if you want to continue the dialogue I'd prefer we kick it to inboxes. Peace and One.