The Revolt of the Three Feudatories was a major early test of the Qing Dynasty, where a number of major Han Chinese viceroys under Qing revolted in a supposed attempt to restore the Ming dynasty. They were led by Wu Sangui, a former Ming general who had ironically enough defected to Qing and won himself power through it. In 1678, six years after the revolt had initially begun, Wu apparently felt confident enough in his position to declare himself Emperor in his own right of the Great Zhou dynasty—but then he died of illness, and his son ordered a retreat that ended in disaster.
So, what if Wu Sangui had lived even five years longer? It seems to my uneducated self that his rebellion would likely still have lost, but it might have lasted a lot longer and have been much bloodier in the end, weakening Qing in a very early stage. Is there any chance Wu’s allies in the Kingdom of Tungning (Taiwan) might have survived as a result?
As it was, the primary issues that erupted within the Great Zhou state after Wu Sangui's death was the contention between its generals over, in general, the power of Guo Zhuangtu, and specifically the contention between Wu Guogui and Guo Zhuangtu over what strategy the rebels should implement, and also the contention over Ma Bao's abandonment of the Siege of Yongxing.
Wu Sangui's successor as Emperor was his teenage son Wu Shifan, who did not rule from Hengzhou, which had been Wu Sangui's capital, but from Guiyang in the southwest. The Southwest was the power base of Guo Zhuangtu, a general who Wu Sangui had appointed to govern Yunnan for him while he was at the front and manage Zhou logistics. Guo Zhuangtu had wanted to seize power after Wu Sangui died, and he decided that the best way for him to do this would be to support Wu Shifan, who was already in the southwest and in a sense Guo Zhuangtu's scion, as a puppet ruler. Since Wu Shifan was Wu Sangui's heir according to the traditional succession laws, the Zhou generals accepted this.
However, Wu Guogui, another important Zhou general who was in Hunan with most of his comrades organising the defense against the Qing offensive into Hunan, thought that the only way for the Zhou to win at this point (by 1679 the rebellion was not collapsing, but it was very hard-pressed by Qing offensives and Ma Bao's abandonment of Yongxing had cost them the opportunity to deal a substantial blow to the Qing army) would be for them to gather all of their troops, including the garrisons that were under Guo Zhuangtu's and Li Benshen's commands in Yunnan, to launch a massive attack on Jingzhou, the Qing logistics centre in the central part of the front. Wu Guogui's "Northern Expedition" plan, as it was called, was supported by Hu Guozhu, another general, who agreed to go to Yunnan to convince Guo Zhuangtu. Guo Zhuangtu argued that if the Zhou took all of the garrisons from their rear areas, they would be deprived of a logistical base, so maintaining the garrisons in the Southwest was the only way to win. Most of the other Zhou generals, including Ma Bao and Xia Guoxiang, agreed with Guo Zhuangtu. So Wu Guogui and Hu Guozhu failed in their attempt to implement a Northern Expedition, and the garrisons remained in the southwest. What ended up happening was that the Qing launched a massive offensive into Hunan that year, which conquered the entire province. Wu Guogui was killed by Qing artillery while defending the fortress city of Wugang in southwestern Hunan.
Wu Sangui's death was certainly a great blow to the rebellion. It was, immediately, the reason why Ma Bao abandoned Yongxing, but the death of Wu Sangui also dealt a great blow to Zhou morale. Right up until Wu Sangui's death, the Zhou were able to, with great effort, repel all of the offensives the Qing threw at Hunan. His death was soon followed by the loss of such strategic points as Yuezhou, which had withstood several years of constant Qing efforts to besiege and take it. So it can be reasonably assumed that Wu Sangui surviving longer would prolong the rebellion. However, I highly doubt it would increase the chances of Zhou victory. It would merely cause the stalemate that existed at his death to drag out longer. I also doubt this would lead to the "Kingdom of Tunging" on Taiwan surviving. The Qing might be too exhausted to take them out right away, but it would only be a matter of time until they were. 1695 is about the latest I could envision Tungning surviving under this scenario.
