Some misinformation here...
Will China change her tax policy again when Japan can no longer support the silver demanded by the state?
Oh, don't worry, because Japan will. Per Von Glahn's magisterial work on the late imperial Chinese economy -
Fountain of Fortune: Money and Monetary Policy in China, 1000-1700 (p. 232) Japan supplied 75% of China's foreign silver in the 17th century. Since the Yungui mines were incapable of even meeting the silver demands of impoverished Yungui, it's safe to say that Japan alone was responsible for selling China more than 2/3 of its silver supplies. This is despite the restrictive policies of the Tokugawa shogunate on Chinese trade. Even in the early 18th century only Guangdong and Fujian were truly dependent on American silver and it was not until later in the 18th century that China was truly dependent on non-East Asian silver. Even without Potosi,
mei wenti until the mid-1600s or so, even if we're factoring in the increased foreign interest in Japan.
do the Ming decide to try to transition back to paper money?
Everyone was terrified of paper money because of its history of hyperinflation under the Yuan, and Japan has enough silver to last the entirety of the Ming, so no. Also, the Ming realized early on with a failed experiment (the
Da Ming tongbao paper money) that paper money would need to be backed up by precious metal anyways to actually be effective.
I think the interest of outside powers in Japan's silver would likely increase.
Agreed.
Spanish silver caused rampant inflation in the Chinese monetary system
There is general consensus that silver, both Japanese and American, greatly aided the Ming/Qing commercial revolution by lubricating the economy with more money. You're correct that inflation was rampant in the last years of the Ming, but the net effect of silver was positive and allowed the 18th century to become the most affluent in all of China's history prior to the late 1900s. Note that China was suffering from a major deflation problem prior to the influx of silver.
just as the Chinese were implementing economic reforms to deal with the inflation
There is no sufficient evidence that silver imports declined greatly under the late Ming. If/when Manila reduced its silver supplies, the Chinese just went to Nagasaki instead. As mentioned, Japan provided most of China's silver. See "Silver and the Fall of the Ming: A Reassessment" by Brian Moloughney and Xia Weizhong, who conclude that "the collapse of the Ming in 1644 was due more to factionalism and nepotistic squabbling [...] than to the vicissitudes of international movements of bullion." Kenneth Swope, a leading military historian of the Ming, agrees (*The Military Collapse of China's Ming Dynasty*, Ch. 8).
Jiangnan's flooding issues
What floods, specifically, are you talking about? And how can you prove that the influx of silver, which was welcomed by Jiangnan's burgeoning economy especially, was responsible for these floods?
a reform to simplify the collection of taxes by accepting only silver in payment rather than the multiple metals or in-kind tribute which had been taken before
You appear to be describing the
Single Whip Reform, which commuted the taxes in kind and labor to silver. That was systematized in the 1570s, more than two generations before the Ming collapse, and was fully established by the 1630s when the rebellions broke out. It is very wrong to claim, as you did, that they were passed "
just as the Chinese were implementing economic reforms to deal with the inflation."
IIRC there was also an anti-corruption campaign of some effectiveness, a land survey to attempt to bring the great houses into line and force them to pay more in taxes, and a cut-back of the bureaucracy to reduce the civil payroll and save money for useful things.
I think you're describing reform movements like the Donglin Party and the Restoration Society, who generally wanted to rationalize the inherently inefficient Ming state (the first emperor made the government drastically more ineffective and made it extremely difficult for his descendants to change it back). They all failed not because of silver or the lack thereof, but because late Ming emperors were all terrible rulers who were not up to the job.
You know, I'm starting to wonder if Potosi produced any actual winners, or if literally everyone affected (Spain, China, Europe, the Ottomans, everyone) was worse off for the influx of silver.
It greatly aided the commercialization of China and Southeast Asia, and many world historians consider it an important factor in Europe's economic rise. You need to look at the broader effects on society, not the short-term geopolitical effects.