In a full scale war with China, I don't think TSMC's fab can be preserved. China can destroy it without landing on the island, easily.

Taiwan is too close to China, that is a reality. Plus, modern chipmaking is an incredible sophisticated business, for example, you need huge amount of electricity and raw materials imported overseas to sustain the fab. When the war breaks, all of that would end.

Their effort should be spent on to prevent the war from happening in the first place, that is the only way to 'win' the war.