Also the other obvious answer that people have been doing for centuries is multi-generational households.

It's not the end of the world to live with your parents (or your partner's).

I think we could see a lot of pressure towards that as Western total fertility rate continues to decrease and larger population groups (Millennials) age with fewer or no children to help out.

Even a shift towards non-relatives households wouldn't be the end of society, it would just be change (and require some zoning/code changes).