What is your opinion about the proposed scenarios? Is it possible for Bitcoin to fall to zero or be replaced by another Cryptocurrency?
Their predictions are fine if that was really based on their study. But that just doesn't always mean it's the truth. There's still a lot of factors to be considered before saying such thing.
It's always possible for any currency to fall to zero value or be replaced by other currency reagardless if they are crypto or not. In the case of bitcoin, just like what other users mentioned above, the probabilty of bitcoin crashing to zero value is near to zero, as this coin is strong and there are a lot of people that are supporting it. That's why it is unlikely for it to have zero value.
Can it be replaced by other cryptocurrency? Yes, but again, it's unlikely, the coin should have a massive adoption(more than bitcoin had), if that happened, that just means that cryptocurrency is way better to bitcoin technology not just as cryptocurrency.
The bitcoin's future is in our hands and no one can predict if it will fall or not. Five to Ten years from now, bitcoin can be successfully replace the fiat or it will be vanished who knows? So if we want for the bitcoin to be successful and well-known we should mass promote it and share our experience to other in order for us to encourage them to join here in crypto world.