alt Hacker NewsLook what happened to many people who broke NDAs or helped to do so. Snowden is stuck in Russia. Assange got holed up in an embassy for years. Sarah Wynn-Williams, the Facebook/Meta whistleblower, got an insane court order against her [1].
Theoretically, retaliating against whistleblowers is seriously illegal stuff. But in practice these regulations are seldom enforced. And even if your (former) employer does not retaliate openly, there might still be "invisible" retaliation, or the risk of other large employers just blacklisting you by default.
Breaking a Google NDA carries substantially less risk than leaking classified information, I imagine. And I would expect that someone exposing true existential risk would receive plenty of support in the face of civil suits. In any case, being more afraid of the courts than the end of humanity (if that’s what they want to leak) surely calibrates how strong their belief must be.