War costs a lot of lives, but a hot war between adversaries means making the adversarial position suffer more for having taken up arms in the first place. A defensive war over Taiwan and keeping our promise doesn’t need a number on the table in advance to make it worth doing. It’s crass to even ask. How many American lives will it take to sink every boat belonging to or commandeered by the PLA in the Taiwan Strait, shoot down every jet that flies above and mow down every pair of PLA boots that lands on Taiwan’s beaches, and destroy every military shipyard on their coastline? Let’s assume this isn’t purely an American fight, you know, for the sake of argument.
If you can figure that one out, you’ll have something close to your answer.
How many people do you think the CCP will sacrifice to take Taiwan?
For instance, just recently the likely next DPP/pan-green presidential candidate is declaring that Taiwan is already de facto sovereign and independent, and so there is no need to formally declare independence:
https://twitter.com/brianhioe/status/1615638156367507456
Odds are, this entire discourse in this HN thread is just a lot of fulminating hot air by people who don't even live in Asia, grognarding hypothetical wargames and war toys, while the actual people in China and Taiwan will peaceably and gradually figure it out over time.