Even if Bitcoin goes to 0 or close to it, it won't happens overnight, so you will have plenty of time to jump off the boat or adapt to the new situation.
And he is not the only one speaking against BTC while BTC grows bigger and bigger
The real question is whether you or I or anyone would recognize that the decline was the end rather than just a pull back and opportunity to buy more at a cheaper price. It's tough when you're in the moment, emotion will take hold and impact decision making.
It's best to know at what point you'd sell out - $200? $100? $50? At what point do you sell all? It's an easy question to answer it's a tough to follow through on.