I think some of it depends on what your definition of God is.
If you see a God as being a concrete, physical being, I would assume they are subject to mortality, like us humans(and everything categorized as 'living' would be). But, even then, all the Gods that have disappeared into time may or may not have existed, much like most of our ancestors have disappeared into time, unremembered(as most of us will, too). No one will remember us, and it will be as if we never existed.
If you see the different 'Gods' being simply one manifestation of a greater God/universal force/etc, the fact that many have disappeared just means that force is chosing(or maybe it has no choice, who knows)to manifest in other ways.
You really want to qualify your statement with "if"? How about "when". The list is quite extensive, to include: slavery, religious intolerance and persecutions, political and racial pogrom, abortion and contraception, separation of church and state, and so on, ad infinitum.
For all the beliefs that do get acted upon(for either positive or negative), there are myriads of other beliefs that don't get acted on. A lot of it depends on how strong the belief, and how much of its permeated into the culture around it.
I get really exhilarated when I find other people who think Star Wars is boring, but I've yet to start a group that wants to see it banned. The belief is not strong. The support is minimal.