Let's assume, when bitcoin is still at $6500 the price of ETH is in the range of $200. Currently bitcoin is at $3250 and the price of ETH have touched $80. So it can be concluded that, if bitcoin touches $2000 the price of ETH will be in the range of $40, and the value of other altcoins will decrease up to 50%. I can't imagine if this really happened, maybe there are will be many investors who go bankrupt and won't believe anymore if cryptocurrency is a profitable investment.