We're not talking about a targeted weapon, we're talking about accidentally unleashing an unstoppable global pandemic. If only China is risking that, the odds are better for everyone.
If they somehow survive of course.
OFC, if any leader worth their salt will respond with "Hell NO, if you threaten us again with that, or we find any sign it is released, we'll nule everything in your land and anywhere it is found. Even if a vaccine/antidote works for humans, destroying the animal & plant populations would just result in the surving humans to die slower of starvation.
Thinking about this for a few seconds, it is really pointless, and maybe one of the most serious examples of "Just because you can do it, think hard about whether you should do it". The answer is Fck NO. (And I'm almost always in favor of tech advances.)