1) There's a difference between an egregor and the collective unconscious. That said, the role of the egregor of a society in its rise and fall is of great importance. When Western civilization was strong, its egregor was intensely appealing, which is why (for example) our ugly and dysfunctional clothing styles got picked up almost everywhere in the world. Now that Western civilization is cracking, the egregor is no longer anything like so attractive.

2) Cultures vary in how much reality testing their egregors get. The Roman empire imploded precisely because some of the core tenets of its egregor were decisively contradicted by events -- it was central to Roman ideology that Rome had been given perpetual rule over the world, but nobody told the Visigoths. Its cultural implosion followed promptly. That example does seem very similar to what we're going through now.

3) Two good questions I can't answer. I'm not sure if anyone can.