X-Men: Dark Phoenix is the end of an era for the second X-Man film franchise. After the Disney/Fox buyout, no one can really be certain just where our favorite mutants are headed--unless of course you count the much-delayed New Mutants which may or may not ever actually see the light of day--though, with any luck, it'll be on to bigger and better things under the shared MCU umbrella for the first time ever. That said, it can't really come as a surprise that the final moments of Dark Phoenix are just that-- there's no post-credits tease or stinger to round off the story and hint at what's to come. Instead, we're left with a superhero rarity: A conclusion that actually seems, well, pretty conclusive.
So what exactly happens at the end of Dark Phoenix and what does it mean? Let's break it down. Warning: There are major spoilers ahead for the ending of X-Men: Dark Phoenix. Stop now if you haven't seen the movie and don't want to know how it plays out.
With Jean (Sophie Turner) rapidly losing control over the mysterious Phoenix Force--though the movie never calls it by name-- and her tenuous grip on her own sanity slipping, she succumbs to the (honestly, pretty half-hearted) manipulations of Vuk (Jessica Chastain), one of the D'Bari--a race of shape-shifting aliens that are definitely not Skrulls, looking to harness the power of the Phoenix Force for themselves to terraform the Earth and remake their lost homeworld.
Vuk explains that the D'Bari don't fear Jean's power like her friends did, and therefore she should trust them--but really, all Vuk wants from her is the Phoenix Force, which Jean nearly gives up. But before she has a chance to do that (and unknowingly doom the Earth) the X-Men interrupt. Half of them want to murder her, the other half want to save her, and Jean doesn't really care for either side of the equation. Also, the humans are less than thrilled with the whole situation--Jean unwittingly flipped some cop cars during her first big clash with the X-Men, so human/mutant relations are crumbling, you know, like they usually are. During the fight, the army intervenes, capturing every X-Man involved along with Jean herself with power neutralizing collars. The D'Bari escape the scene but quickly chase after Jean.
The action culminates in a massive battle on a train in which the humans must be convinced that the X-Men can protect them from the D'Bari while the D'Bari hurl themselves Terminator style into the fight, trying to get to Jean, who spends most of the final battle unconscious. That is until Xavier, with Scott's help, manages to reach her cell and wake her up. (It should be noted that the humans the X-Men convince to free them still wind up dead--so, uh, it turns out the mutants weren't all that great at protecting them after all.)
Emotionally moved and imbued with a new sense of purpose, Jean confronts Vuk for the final time, producing a whirlwind of neon destructive force around the two of them that threatens to disintegrate everyone and everything--including Jean's friends. With no other recourse, and no hope to be rid of the Phoenix Force all together, lest it fall entirely into Vuk's hands, Jean opts to blast the two of them into space and sacrifice herself for the safety of mankind.
In the last few moments, the X-Men watch helplessly from the ground as a supernova shaped like a phoenix (get it?) explodes in the sky, consuming both Jean and Vuk safely outside of Earth's atmosphere.
But of course, things don't actually end there. The remaining X-Men are left to pick up the pieces--sort of, at least. With Jean and the Phoenix Force gone, the government seems to be back on great terms with the mutants (never mind the shockingly high human body count), meaning everyone is apparently just fine and dandy to head back to Westchester and get their affairs in order. The Xavier Institute is renamed the Jean Grey School in honor of Jean's sacrifice, Hank takes on the role of the headmaster, and mutants like Storm begin as teachers for the next generation. Professor X himself retires to Paris, where he meets with Magneto for a game of chess, just like old times--all while a suspiciously Phoenix-shaped neon flare blasts through the sky overhead, implying that Jean may still be out there somewhere. Magneto also hints that Charles could come live with him, assumedly on his mutant refugee island.
All in all, it's a pretty tidy ending--the majority of the "First Class" has either moved on or died, tragically, but the dream of the X-Men continues in the hands of some alumni and the memory of Jean. Human and mutant relations are, we can assume, looking pretty good and Charles and Erik have found a way to start resolving their perpetual conflict peacefully. All things considered, it's not a bad way to leave things, especially considering that Dark Phoenix is very likely the swan song of the non-MCU X-Franchise as a whole. It's a safe bet that we'll be seeing some mutants again at some point in the future, but this particular era has definitely run its course.