The problem is the political implications... for one, it would send a signal to China that a land-grab against Taiwan will yield a bit of trouble but nothing too serious. That's the worst case and I seriously hope that that alone (and the economic devastation associated with TSMC blowing up their fabs to prevent them from falling into Chinese hands) is enough to keep the support going.

The other factor is that it might lead to a complete fracture of the NATO - Finland, the Baltic nations and Poland will not accept any kind of Russian success out of that war. They're all no big economic players in the EU/NATO, but a major internal dissatisfaction in NATO may entice other players in the world to play rough again as well, not just China.

Ukraine gave up their nuclear weapons and long strike weapons in exchange for a promise to not be invaded.

After Russia broke that promise who would ever make that same deal again?.