If it is war then China must telegraph to the U.S. now that an end to strategic ambiguity means war. (And this must be done before strategic ambiguity actually ends.) Because otherwise I can see the U.S. deciding to do it. Once this is done, use of force from that point on would become insane; it would invite WW3.
This is what China has been saying for years.
Whether anyone is actually listening is another question.
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Let's suppose the US was to end strategic ambiguity and announce Taiwan would be recognised/defended.
There's all sorts of scenarios where China could assert sovereignty.
For example, China sails some ships within sight of Kaohsiung or Hsinchu or Penghu
The Chinese Coast Guard alone have many more ships available than the Taiwan or the US. Plus some of these ships are larger than any Navy destroyer or cruiser.
So no-one else is able to shove them out of the way.
The US and Taiwan would be shown to be impotent in such a scenario, and the general population would likely start panicking at the sight of Chinese ships hovering within sight of the coastline.
Are Taiwan or the US really going to start shooting at Chinese Coast Guard ships over this, and start an actual war?