It dies when governments make it illegal, and so hard and expensive to use, that the cons far outweigh the pros. One such scenario would be if crypto suddenly

It dies when governments make it illegal, and so hard and expensive to use, that the cons far outweigh the pros. One such scenario would be if crypto suddenly became a real threat to whatever fiat a country uses. If BTC became a legit threat to USD, you can be sure the gov. would do everything in their power to remove BTC. Maybe a realistic example would be if, say, BRICS countries suddenly colluded to stop using USD, and only use BTC as a currency.