They definitely gonna destroy them if they sees the stablecoin owned by private company could conflict with their interest, imagine what action a government would take to get back all the market shares for it once they figure out that their CBDC most likely not gonna be as popular as the already established stablecoins.
Of course, I doubt about destroying stablecoins, but they will take measures for sure. They will impose taxes, introduce some prohibitions. Some countries may ban the whole thing in principle
Definitely taxes at every corner so they can make profit off it the same amount generated from their own version of stablecoin this so called CBDC. but I'm pretty sure most of them gonna oppose the idea of private company trying to compete with them, after all most of government likes to monopoly things.
Just wait until all these CBDC released to public it's gonna shake the whole crypto market not because its usability but because the fuss about regulation around it.