hmm I just thought of something particularly interesting to me. The Goa'uld were supposed to be the gods of many major polytheistic religions on Earth, as the Asguard were for the Norse.
But if you look at history in the late BC's and early AD's monotheism is on the rise. It becomes more and more prominant. Now if Stargate were in the real world (really really big if, but go with me on this) could this correspond with the Goa'uld and Asguard leaving Earth?
You know, without their influence on their own religions it might fail in favor of some other religion.
Eh just stating my random observation