And as with Google and Stack Overflow before, the Sr Devs will smack the wrists of the Jr's that commit untested and unverified code, or said Jr's will learn not to do those things when they're woken up at 2 AM for an outage.
To be clear, I think any business that dumps experienced devs in favor of cheaper vibe-coding mids and juniors would be making a foolish mistake, but something being foolish has rarely stopped business types from trying.