or would people revert to gold instead?
I am assuming that by catastrophe, internet will also be lost. Which means this is a completely useless question since bitcoins together with all the other altcoins out there would clearly sees to exist and will be easily forgotten in a few years time after the said catastrophe. But, if you mean a catastrophe that exempts the internet usage, then I pretty much think that bitcoins would still have value since it will be the one that can be easily used to send value across the globe. It will be a good payment for labor and other things. But even so, in remote areas, I think that barter trading would be the most logical thing we can think of to happen.