In a nutshell, Bitcoin would adapt.

Let us consider the actual ramifications of this scenario. At present, we have seen so called "mining bans" occur with the predictable impact on price. The psychological impact of news like this is the biggest component; confidence in Bitcoin is undermined whenever significant, especially restrictive regulation hits the news cycle. The network itself never suffers any real harm, and the hash rate eventually balances out as miners simply move to a new jurisdiction where mining is permitted.

So what about a scenario where mining is outlawed on a global scale? Be it due to environmental concerns, financial regulation, or any number of unforeseen reasons? Always remember, bitcoin is a living and breathing thing. If the consensus method (proof of work) is the problem, we can easily fork and change to a new method. It's hard to believe that the community would give up on this grand experiment so easily, given the trials and tribulations we have gone through so far to get here. Bitcoin is far from set in stone. And as it continues to evolve, we will undergo a number of radical changes to create the most perfect network we can achieve.