For me no, the existence of belief, and the actual existence of the subject believed in are not related. Otherwise all kinds of insane fairytale characters like Santa and the Easter Bunny would be running around.
Belief in god and religion for me has always been about three things. The first as a way for uneducated civilisations to explain natural phenomenon such as the sun and moon. They can't explain it, it seems all powerful, it's a god... i guess you could also classify creation of life under that too.
Then there's a persons natural need to search for something better in life to latch onto to give them hope, so for example whether that's personal tragedies, addictions, or the unforunatate circumstances you were born under. Country at war, extreme poverty, dictatorship etc.
Then there's the standard practice of passing belief onto children. In countries like England, where christianity really isn't a factor any more for the majority of people, the 'belief' isn't passed onto easily susceptible children, and starts to die out. This practice isn't just related to religion, but any social situaion. For example in simplistic terms, if you tell a enough children white people are better than black, they'll believe it and a racist society will grow. Places like the middle east, and america, where religion is still a massive part of adult life, means it's passed on to children, and the cycle of belief continues.
So for me there's really no relation to mass belief in deities making any difference in the chance of one existing.