whoever said bitcoin will be worth $100k on one day is nothing more than a dreamer living in a fantasy world. predictions up to $5K are also high, but not that unreasonable. $100k is beyond insane.
$1000 per btc was 'beyond insane' when it hadn't even reached dollar parity. One thing I have learned is that anything is possible.
You are absolutely right, anything is possible, including the drop to 0.
Yes, there is a non-zero chance that BTC will be valued at less than a dollar. However, considering most dead alt coins are still worth fractions of a penny I don't see the probability of it going to '0' being very significant.