That's a lot to unpack, and the plot is complicated by the density of action. There are plenty of revelations within the last three episodes of the show, like the fact that both telepaths, Thale (Sam Strike) and his handler Dr. Agatha Matheson (Gretchen Mol), can astral project; the fact that the handsome Captain Roy Eris (David Ajala) is actually an extremely old man who lives in a tube; the fact that Eris and his lover Melantha Jhirl (Jodie Turner-Smith), genetically engineered from birth to be an ideal astronaut, are actually siblings; and the fact that Karl D'Branin (Eoin Macken) figures out that the volcryn presence outside the walls of the ship is able to transport him to a parallel timeline in which his daughter never tragically died.
It's this last detail that actually has something to do with how the story ends. Karl steals an escape pod and shunts himself into the mouth of the jellyfish-like volcryn, ending up getting blinked out of existence in this timeline and into what appears to be a different one, where his daughter runs out of her room to hug him and welcome him home. Meanwhile, the Nightflyer, reeling from Cynthia's sabotage, is swiftly overheating, its nuclear reactors threatening to explode and destroy it and the alien life form outside. Lommie's consciousness, trapped inside the ship's computer, is able to completely shut down all systems while the remaining crew huddle together for warmth in the mess hall, sending the Nightflyer tumbling toward whatever awaits it inside the volcryn beast.
There's a lot of nonsensical storytelling left unexplained. Why give two characters the ability to astral project, only for one to kill herself and the other never to do it again? Why have one character go on a murder spree for an entire episode, then act like it never happened? Why end on such a massive cliffhanger? If the answer to these questions is a second season of Nightflyers, expanding beyond George R.R. Martin's creepy source material, it offers an opportunity for answers further down the line. But for now, it's left so open-ended it lends itself well to plenty of fun theorizing.