Bitcoin can not drop to zero, it is not like other altcoins that does not have value in the market. If Bitcoin is experiencing the bear market that doesn't mean the price of bitcoin will drop to zero. It is only shit coins that have the tendency to drop to zero.
You are right bitcoin cannot drop to zero, bear market will make people think that bitcoin will drop to zero meanwhile dip is highly required after a huge pump, bitcoin was once at $50 per unit, now its worth more than $20k, such an amazing increase, and if bitcoin tries get back to $10k lots of people will be thinking bitcoin will go to zero which is not possible, for a healthy growth of the market a correction is highly important, which tends to be the bear market, soon bull market will arrive but no one knows when