I see- I agree this wouldn't work if there was a _catastrophic_ break in the crypto algorithm... My post assumes that if the algorithm is broken, it would mean that questionable bitcoins could be created at a higher-than-expected rate, but that there would be time for people to backstop it by updating their clients. I would think that a less catastrophic issue (leading to only an order-of-magnitude improvement in hash solutions) is more likely, but I suppose a fully catastrophic break is also possible.