I'm pretty sure that the Chinese government is actually scared shitless that Taiwan declaring independence would reinvigorate independence movements in Hong Kong, Xinjiang, Inner Mongolia and probably half a dozen more.
A new civil war in China would make WWII look like a minor scuffle.
Why would they be "scared shitless"? They've demonstrated the ability to crack down hard and defeat those movements. For instance: the Hong Kong protests ended almost immediately once China decided to take the gloves off.
Maybe they could control simultaneous large scale insurrections. But it would be wise not to be overconfident in that regard.
Why do you think they'd have to deal with any "large scale insurrections"? They easily delt with one HK, once they imposed a Mainland-style security law, because fear evaporated the protests. Those protests also didn't inspire much of a response in the Mainland. They also didn't have to deal with on in Xinjiang, where they implemented so much direct oppression that you'd think they'd have inspired a response if one were possible.
The PRC security apparatus is strong, well organized, and its actions aren't constrained by liberal sensibilities. The PRC population is thoroughly disarmed, disorganized, and dis-informed, so cannot resist it. I think you're indulging in wishful thinking and fantasy.