No, I think they're really onto something there.
S3 ending spoilers
Catra broke reality, which dropped everyone into a "perfect" sort of "dream reality", which was collapsing, but none of the happy dreamers could see the collapse, people and places just disappear and the dreamers continue on happily as if those things were never there to begin with.
When a dreamer confronts the facts of their real reality, particularly tied to strong emotions, they see flashbacks, their eyes widen, their eyes dart around, and then they wake up and gain the ability to see the world crashing down around them (even if the crashing world takes them out).
King Micah is the only "dead person" in this dream reality, and he's presumably only there because his "life" creates happiness for Queen Angella and Glimmer.
Angella wakes up when she confronts the woke Glimmer. But she hesitates to do anything about the end of the world which see can plainly see, because she desperately wants to stay in the dream with Micah. But naw, she says goodbye to Micah (even though it hurts) and she's gonna go save Glimmer who really needs her in the real-reality.
"Dream Micah" was told by Adora that he's dead in the real reality, and him and Angella had some time to try and process that. But nah, that can't be true. Micah and Angella both reject that info and refuse to wake up. But then... the woke Angella says her goodbyes and flies away.
At this point, Micah's eyes dart around. It's exactly how a waking dreamer acts in this world, minus the audience being shown his flashbacks. And then he yells "Angella wait! I'm not...!" before he gets swallowed up.
I can't see any reason why a "not real" Micah would act like that, while "I'm not dead!" would be the perfect thing for a real, not-dead Micah to yell in that situation. He wasn't killed, he was captured. He's on Beast Island (where Entrapta is headed now).
I totally expect Micah to show up later. He'll probably have something to do with Shadow Weaver's redemption arc. And then Angella will show up again because of portal shenanigans.