We have engineering practices that guard against humans making mistakes that break builds or production environments. It isn't like we are going to discard those practices. In fact, we'll double down on them. I would subject an LLM to the level of strict validation that any human engineer would fine suffocating.
The reason we trust compilers as a black box is because we have created systems that allow us to do so. There is no reason I can see currently that we will be unable to do so for LLM output.
I might be wrong, time will tell. We're going to find out because some will try. And if it turns out to be as effective as C was compared to assembly then I want to be on that side of history as early as possible.