People in entirely different societies under entirely different pressures have done very much what Heaven's Gate did, in whole or in part. In Heaven's Gate, you had something close to the Platonic ideal of a passive millenarian movement. You will learn little about America or late modernity from studying it. You will, however, learn a great deal about one of the more dreadful capacities of the human condition. M illenarianism is not an attribute only of cults or small sects.
Whole societies can become millenarian for decades at a time.
When that happens, some version of apocalypse is often enacted in literal fact. In Christianity, millenarians usually look forward to the Second Coming of Christ after a period of tribulation. Christian millenarians in the United States have traditionally been politically passive, though this is changing with the increasing political mobilization of the evangelical vote. Some millenarians, on the other hand, form revolutionary armies, like the Fifth Monarchy Men of the English Civil War. These reactions are really matters of degree.