Europe doesn't have the capacity to impose a no-fly zone on Russia. I doubt even US could pull that off.

Anyway, the real concern wrt nukes is that they require people in government who are at least marginally sane and care about self-preservation. The problem with countries like Russia and Pakistan is that it's one coup away from being run by people who genuinely believe that they are fighting a holy war against some kind of worldwide Satanic conspiracy. Such people are unlikely to hold power for long, but with nukes, they don't have to.