There are possible scenarios for how the world would "crash".
1. We run out of fossil fuel, people start fighting for the last remaining bits of it. Governments get over run by the people, all out war happens across the world. To be honest, if governments were overthrown, I'm not sure how that would go, or if it would even be possible, but for conversation sake, it would prolly be anarchy. there wouldn't be many followers of the group that overthrew the government, people would start doing their own thing, which would turn into something like what you said. People arming themselves and putting up defenses and creating their own society.
or
2. Religiously speaking. The bible is correct (lol). Armegeddon hits, detroys all organizations, governments, laws etc. We clean up the earth, live under god's rule, become perfect again ...
or
3. We fuck up the earth so bad that it becomes unlivable. Iono if the space idea is ever going to pan out like you see in movies, doubt it. But I really don't see how we would survive by fuckin up the earth.
All in all, end of the world comes, you can see alot of people digging in somewhere and telling everyone to fuck off lol.