It's complicated because 'god' can fall into many categories, and the categories themselves vary. I find it very possible that an extra galactic being can pretty much do what ever it wants; however it doesn't mean it's immensely or infinitely knowledgeable, and powerful. I think humans can pretty much become gods of their own, it's not the first time tribes thought that white people were earth-locked spirits simply because they're pale and have reflective items like a watch or a mirror. I'm going to say that true gods don't exist, but superior lifeforms can and will.