Blockades are considered acts of war. Taiwan would be within their rights to sink any ship blocking their ports.
Actually I would expect China to use either chemical or biological weapons against Taiwan. Perhaps a more deadly version of the Wusan virus. Let that loose in Taiwan and the world would block Taiwan for China.
Which that effort would be in vein. Taiwan would hope that the west would intervene - which it wouldn't.
Don’t overlook the fact that for all the influence China has bought in the USA, they have bought many times more in the Taiwanese government. Reunification will eventually be marked by a treaty signing ceremony, rather than a military invasion.