Thanos Ensues

Reality Ensues is when an outcome to an event, or a consequence to someone's actions, happens because This Is Reality and it's meant to be a "realistic" outcome.

This is the exact opposite.

This is an outcome that happens (or fails to happen) because the work ISN'T realistic. Science fiction, fantasy, a combination of both, or a Planet Eris means what's "supposed" to happens makes way for what would actually happen given the bizarre nature of the particular universe.

Often happens because the characters in question are Flat Earth Atheists, Locked Out of the Loop, or just plain Genre Blind.

SPOILERS AHEAD.

Examples of Thanos Ensues include:

Anime and Manga

• In a realistic work, Chichi would be in the right. Unfortunately, in that universe The World Is Always Doomed, and Gohan being a Saiyan means he is one of the few beings powerful enough to keep Earth from being destroyed.

Animated Film

• The argument in My Little Pony: The Movie doesn't last long because the universe is one when The Power of Friendship prevails over anything (hence the source show's subtitle, Friendship is Magic).
• The consequences of The Incredibles believing themselves to be superior over Badass Normals are never explored because Brad Bird confirmed that the overal message is about family, so the superhero stuff takes a backseat to that.
• Zootopia avoid the logistics that would result from a truce between predator animals and prey animals because the movie is a Buddy Cop Movie meant to push an anti-discrimination Aesop.

Live-Action Film

• The Trope Namer isAvengers: Infinity War, and the overall Marvel Cinematic Universe. The fallout of Captain America: Civil War is meant to be Reality Ensues: the Avengers are split and Iron Man and Captain America are at odds with each other....and then Thanos invades the Earth with the Infinity Gauntlet and the Infinity Stones, showing that the MCU Earth can't afford the luxury of having the Avengers split due to a bigger threat always looming on the horizon. This also means that Helmut Zemo failed, since he never took Thanos into account. By the end of Avengers: Endgame, this trope is set in stone: the Sokovia Accords are abolished, Tony Stark dies before he has a chance to confront Bucky, and thus all the Reality Ensues revolving around Captain America: Civil War goes right down the drain.
• This very much holds true post-Endgame: despite the Accords being name-dropped, they are obviously not the same Accords as before, and the "Pro-Bucky/Anti-Thaddeus Ross heroes VS Anti-Bucky/Pro-Thaddeus Ross heroes" conflict is no longer present.
• The scene in Rogue One with Darth Vader delivering a Curb Stomp Battle to a squadron of Rebels is meant to cement in stone that no matter how corrupt or inefficient the higher-ups at the Rebel Alliance gets, The Empire will always be the Big Bad of Star Wars, since the franchise is a Space Opera where War Is Glorious.

Literature

• Any attempt in Harry Potter at showing the psychological scars that would result from Harry being forced into the role of The Chosen One and/or forced to endure the Dursley's abuse gets sidelined the next time Voldemort and/or someone acting on Voldemort's behalf starts wrecking havoc with magic, because in the Potterverse "magical" problems are far more important than "mundane" ones.
• In Twilight, the consequences of an abusive relationship are never explored because Edward is a vampire and the whole saga is a Gothic Romance.

Live Action TV

• A common issue in Once Upon a Time, since the "realistic" settings of Storybrooke and Hyperion Heights are window-dressing for the fairy tale/Disney/literary Massive Multiplayer Crossover. A recent example is the Candy Killer Arc, with the Candy Killer being a fairy tale character who targets witches rather than a "mundane" serial killer.
• The massive amounts of collateral damage the Power Rangers often cause is either ignored or Hand Waved away because the show is a superhero show aimed at a family audience.
• The attempts at Revisiting The Roots in Arrow failed because the Arrowverse became a Planet Eris after the introduction of The Flash, and there's no turning back. The writers eventually realized this and brought back the "comic booky" elements to the show.

Web Comics

• Scary Go Round has a Kudzu Plot that runs on science fiction and fantasy tropes, so Erin Winters' story, which runs on Slice of Life tropes, is sidelined and then brought to a screeching halt.
• Despite the goverment being constrantly portrayed as being corrupt and/or inneficent in Spinnerette, the consequences of this are never explored because, even at its darkest, the comic is still meant to be a superhero parody.

Western Animation

• In Justice League, the conflict between Cadmus and the League lasts until Brainiac attacks, at which points Cadmus is forced to admit that superpowered vigilantes acting outside the law to protect the Earth are preferable to leaving the Earth unguarded against "supervillain" threats.