I've been wondering about this.... I mean, I assume we are all in this for the long run because we believe that cryptocoins have a future. If we are wrong and the coins go to zero... then yes, ASIC's and such will drop in value to 0.

But let me ask you... given that we know there are probably hundreds of thousands of GPU's out there dedicated to just mining. If the value goes to zero and mining has no value... what will happen to those cards?

People will dump them and they will flood the market... and granted the market for GPU's is much bigger but still relatively small. Your R9 290x will be going for 1/5th of what it is worth because EVERYONE will be dumping them.