Perhaps I should expand on my first reply:
Atheists to not believe a god exists. This includes many different concepts of god, not your particular fantasy. We can guess at your fantasy, but you didn't specifically define it.
If you *had* specifically defined your concept of God then asking how we would be exactly like that concept is pointless. You must be asking what our concept of a god is, and I don't have one. Remember, I don't think any exist.
A third option that actually might be considered is to consider how we would act or behave if we were different in an important aspect. Many here have pointed out that some aspects are impossible to reasonably consider, such as omniscience or omnipotence... even immortality may be difficult to conceive. The problem is that everyone is guessing at aspects of what you consider to be God, because you didn't specify any differences to consider. It would be equally reasonable to investigate how I would act if I had the burning desire for human hearts of an Aztec god.
In this case you would be asking how someone would act if they are "different", either in one of an infinite ways, or in every way in which case they wouldn't really know. The topic is poorly defined to the extent of being no topic at all.