A quick ban would make a tsunami on western markets, because of the negativism and because traders would expect a fast influx of sell orders of bitcoins from China on western markets.
But a slow death, with lower volumes, lower demand caused by the end or lower influx of CNY and a continuous drop of price on chinese exchanges, with chinese traders cleaning their portfolio of bitcoins, would be worst. It would be another Gox on our hands.
This is whats been happening for the last few months..