And how good your employees are... How good your review process is... How good xyz is...
If your engineers are so solid, and them making a mistake on a given release is individually 0.5%, and you have 50 engineers, you will see the probability of nothing going wrong is about 77%(0.995^50), and something going wrong is 1-0.995^50. Pretty low, i might say.
Dont do this to your engineers. 80% test coverage is a sweet spot, the rest is caught better with other approaches. No reason to kill engineers productivity everytime something fails on production by blaming their tests arent good.
That depends on how good your tests are.