First of all, how is China going to declare ports and airports on Taiwan be close when it doesn't have control over it???
Secondly, its not about the economic damage it can incur on Taiwan, that is probably already being part of the DPP-US-Japan calculus. If they (US-Japan) really wants to press that button, they are are already prepared for the consequences and its eventuality. The sad part is that Taiwan will most likely be sandwich in the middle, the sacrificial lamb.
Like I said before, the reality is that for the US and Japan, China right now is a emergent threat that can be deal with, instead of an existential threat that has to live with in the future.
But a ship owner who knows that all his ships will be arrested that enter a Chinese port, and perhaps when they enter a port in one of the SCO or BRICS countries, if one of his ships entered a Taiwanese port after it was closed will need very little time to reach the right decision. So it will be very difficult to start a war based on anything DPP might do.
