As a manager, can confirm. By the time you get to this point you are being "managed out". There is a basic expectation that you will either leave (preferable) or be fired at the end of the PIP process.
I've heard of people coming back from it, but it's rare. And I think it would need to be the trigger for some kind of personal epiphany that completely changed behaviour for that kind of effect.
I only have a data point of 1 on this so it may be different than other companies, but by the time I'm implementing a PIP, I've already made up my mind that I want the employee out. I've already worked on coaching them and identified that it isn't a temporary issue or something personal they're going through outside of work. HR is my last resort and a PIP is merely a formality I'm forced to deal with. There is a world in which they kick things into high gear and turn things around, but I've usually given up hope and the onus is on them to prove that they are capable.
I've heard of people coming back from it, but it's rare. And I think it would need to be the trigger for some kind of personal epiphany that completely changed behaviour for that kind of effect.