Throughout Westworld's second year Bernard, with his jumbled memories from multiple timelines, continuously asked, "Is this now?" In the season two finale the answer turned out to be yes, as the show finally seemed to leave the past behind as Dolores, robo-Charlotte, and Bernard escaped the park and entered the present day real world. Then the post-credits scene changed the question entirely when it flashed forward to a future where a host/human hybrid William is trapped in a continuous loop. The new question isn't "When will that happen?" though, but rather "Will that be how the series ends?" Because if William is locked in that moment it means Dolores will not only win, she will get the ultimate revenge on her former captor.
Early in the episode Dolores came upon the Man in Black losing his mind as he dug into his own arm to check if he was real. She had already come across the body of his daughter Emily whom he'd killed, so she knew just how far gone he really was. Rather than murder the man who had spent decades torturing her though, Dolores let him live long enough to help her find the Forge, and for him to fall for her loaded gun trap (uh, good thing for her he waited the perfect number of bullets to attempt a head shot.)
With a one-handed William on the ground it seemed like he had finally come to the end of his story, but instead she leaned over and said, "That's what you want isn't it? To destroy yourself. But I won't give you that peace. Not yet." That "peace" was something he couldn't give himself last week when he tried to put a bullet through his own brain, so she rightfully recognized he yearned to finally be free.
After Dolores and Bernard left him behind it appeared William was heading to the Forge to try and stop them, but when the elevator doors opened again he wasn't on it, revealing it was yet another blurring of timelines. It wasn't until the end though that we saw just how far apart those moments were when William entered the Forge and found decades of decay and an ageless host version of Emily. He instantly recognized what that meant. "Oh fuck, I knew it. I'm already in a thing, aren't I?" he asked, thinking his consciousness was inside a virtual world, the kind we saw Ford and Delos in.
"No, the system's long gone," said host Emily. She went on: "This isn't a simulation William, this is your world--or what's left of it," before she brought him into a room exactly like the one he used to keep the failed reincarnations of his father-in-law James Delos.
This version of William is physically in "his park," experiencing this moment "again," since Emily reveals he has been tested for "a long time." Just like the park's hosts, he's trapped in a loop, destined to repeat the same story over and over again. And if the virtual reality Logan is correct, humans always end up at the same point, meaning the Man in Black is doomed to always end up at this same horrifying conclusion that also makes him face the fact he killed his daughter. That alone would be sweet justice for a man who built the nightmare world for the hosts, which he made worse as the villain, but William's fate is so much worse than that.
"Emily" asks him what his entire purpose was in the park, saying, "Tell me, what were you hoping to find. To prove."
Williams responds, "That no system can tell me who I am, that I have a fucking choice." But if that were ever true he clearly doesn't have a choice now. This is a system designed to show him he has no freedom, and more importantly, no escape.
This is happening decades into the future though, so who cares enough to torture him like this, possibly for eternity? Who would even have the ability? The only answer is Dolores, but only if she wins her war. Whether she overcomes Bernard's best efforts to stop her from destroying humans or merely gains control over the park itself one day (very feasible since she now controls "Charlotte"), no one else would trap William like this, especially in such a poetic way. He made her kind his slaves, and to get revenge, she locked him up in a nightmare inside his own park. He wanted control of Westworld and his life, but she has made sure he will learn again and again he has none, all while he is denied that peace he craved.
At the end "Emily" tells him they have to check his "fidelity," but what cause or belief are they checking his faithfulness to? They are checking his fidelity to his own failures as a person, which will forever keep him trapped in Dolores' prison, because just like all of those versions of James Delos ended up at the same spot, William will always end up back here to learn the same horrible--and final--lesson forever: he was never in control.
"Is this now?" For the Man in Black the terrible truth to that question will always be yes, and that might mean we already know how Westworld will end.