1) agreed, but that run doesn't necessarily cascade to another exchange. If the value of btc collapses and people make a run on it, those other exchanges will likely be able to cover the bid/ask spread in any case because by and large they are merely mediating exchanges of $/btc that other people are holding.
3) the 'rational world' was meant to apply to the rate at which bitcoin recovers. In a rational world it would be instantaneous, we're not. It's certainly possible that bitcoin will go to zero as a result of this, but I treat that as a separate case. If you think that bitcoin will survive in the medium-term, my point is the resulting value should be higher than before Mt Gox. In a 'rational world' everyone would figure this out tomorrow, for certain values of irrationality it takes longer for this to suss out, and for extreme values, it goes to zero too fast.
3) the 'rational world' was meant to apply to the rate at which bitcoin recovers. In a rational world it would be instantaneous, we're not. It's certainly possible that bitcoin will go to zero as a result of this, but I treat that as a separate case. If you think that bitcoin will survive in the medium-term, my point is the resulting value should be higher than before Mt Gox. In a 'rational world' everyone would figure this out tomorrow, for certain values of irrationality it takes longer for this to suss out, and for extreme values, it goes to zero too fast.