If one would crack Bitcoin they would be stupid to drive the price to zero. You don't kill the goose that lays golden eggs.
Who says Bitcoin can't change it's proof of work algorithm?
BTC is destroying the traditional central/statist banking model and poised to begin the same process of disintermediation for stock exchanges. Central banking and financial markets are two geese which lay very large golden eggs for some very powerful status quo powers that be. They have an overwhelming interest in killing BTC before it kills their ability to collect rent.
If you are long Litecoin or otherwise short BTC, driving the price to zero would make you a fortune.
If BTC changes its PoW algorithm, it's not longer BTC because the ASIC-based infrastructure currently securing its blockchain would be useless.