Mt. Gox disappearing is good for BTC. From what I've been reading, people who left their money in Mt. Gox accounts have mostly been blaming themselves for trusting an untrustworthy organization. The signs were all over the place that people should pull their money out. And judging by the decline in volume at Mt. Gox, it seems most people did already. And observers need to know that these exchanges are not secure places to keep their money.
Anyone who willingly lets someone they hooked up with over the internet hold hundreds of thousands of dollars of their money should know the risks involved.