First, clickbait headline much? The actual statements by the PRC seem much more reserved, as par the course. Though I guess different people have different standards for "outrage."
That said, I don't think Mattis' statement means much in the long run. The US has been affirming its commitment to Taiwan even after it recognized the PRC, and it will do so even as it also affirms its commitment to the One China Policy. (Remember when Trump's major scandal when he called President Tsai and questioned the OCP? That turned out to be a whole bunch of nothing as he too reaffirmed it.)
Anyways, the PRC will remain hellbent on reclaiming Taiwan and when there's a will, there's a way. Given the increasing disparity between the two, said reclamation is inevitable. Let's all hope that it's a peaceful one, where the PRC respects Taiwan's unique features a la Hong Kong and Macau.
Taiwan is not not going back, and any situation where they end up like Hong Kong would be a complete betrayal by the free world.
