Remind yourself, if your statement is true, you would accept a 1:1000 asymmetric bet on this. Are you sure that would be a good idea?
Just a reminder: be careful when assuming something like 99.9% probability. That's a whole lot of room for improbable events.
The overall probability of a disastrous scenario is course much higher just like you explained. We could see a technical breakdown or a successful attack against the network, or we could see BTC/USD trade made illegal. Anything can happen that would justify a very significant drop in price. But I won't even entertain such predictions until something actually happens.
Everyone knows Bitcoin is a risky investment in general, I'm prepared to lose everything. But to be completely honest, I give EUR a lower survival chance in 2012 than I give for Bitcoin. Euro could completely die, it's very unlikely that Bitcoin completely dies.