We'll all die. It's not so terrifying as depressing. Clathrate gun means death for essentially everyone. Maybe Bezos and Musk are right to make off planet life temporarily viable. Modern society is based on relatively predictable large scale agriculture being able to redistribute goods (transportation infra, tech to support distribution). We simply, as a society, are not capable of adapting to those circumstances. Most humans would die and the survivors would not enjoy a modern lifestyle.