When it comes to flawed big screen superheroes, Marvel has always been top dog. There’s Iron Man, the billionaire, genius and philanthropist who nevertheless struggles in his private life (and once almost accidentally caused the destruction of humankind with his techie meddling). There’s Spider-Man, the young hero who seems to find defeating bad guys a whole lot easier than negotiating the complexities of teenage life in the Big Apple. And there’s Thor, whose original concept of heroism clashed so badly with that of his dad Odin that he was cast out of Asgard for being a pompous gasbag.

Mistakes, for Earth’s mightiest heroes, seem to come with the territory. And yet ever since Robert Downey Jr’s Tony Stark first climbed into his shiny red suit almost a decade ago now, the studio behind the Avengers has refused to make any major blunders of its own. Apart from the odd early gaffe (The Incredible Hulk) and mid-period folly (Thor: The Dark World, Ant-Man) Marvel has pursued the task of creating a credible universe for its superheroes with a remarkable knack for mostly getting it right. Even the dimmer instalments failed to knock the wider galaxy of shiny superstars off course, largely because Marvel always seems to have something bigger and brighter waiting to be released. Thor 2 was followed into multiplexes by the double whammy of Captain America: The Winter Soldier and Guardians of the Galaxy, while Ant-Man segued smoothly into the hard-hitting superhero smack down of Captain America: Civil War and the mesmerising comic-book head movie known as Doctor Strange.

Like a football manager who effortlessly integrates his latest £100m signing into an established team of champions, Marvel supremo Kevin Feige has gently introduced new heroes such as Strange and Tom Holland’s Spider-Man to the ranks of the Avengers without risking the overall balance of the team. The key has been meticulous planning and a refusal to rush movies into production, two basic rules of engagement that rival DC has singularly failed to follow (and reaped the consequences).

But there’s an argument that Feige et al face their greatest challenge yet following Disney’s $66bn purchase of 20th Century Fox last month, which brought the X-Men under the same big-screen banner as the Avengers (just as they are in the comics) for the first time in the modern era, and presumably means there is nothing to stop Disney-owned Marvel from incorporating Fox’s legions of mutant superheroes into the wider MCU.

The clamour for Wolverine, Deadpool and co to appear in Marvel films has already begun. But Feige would be wise to continue the softly softly approach that has served him so well. Because the X-verse, such as it is, has the potential to ruin all the hard work Marvel has put into the MCU up until now if it is not integrated properly.

Whereas Marvel has been set up from the beginning as a unified space for its heroes to have adventures in, Fox has approached its rights to the X-Men in a far more muddled way. While the main X-Men series all sit together on the same timeline, movies such as Logan and Deadpool are far less conclusively part of the same universe, to the extent that different actors (Tómas Lemarquis and Stephen Merchant) played mutant Caliban in X-Men: Apocalypse and Logan, even though the two films were released just nine months apart.

Fox currently has X-Men movies Deadpool 2, The New Mutants, Dark Phoenix, Gambit, X-Force and the James Franco-starrer Multiple Man on its slate. Of these, only Deadpool 2 and X-Force are likely to boast the kind of joined up thinking that is a cast iron requirement for inclusion in the MCU. The New Mutants does not even fit the same genre as its stablemates. Josh Boone’s tale of four young people with nascent powers who have been trapped in a mysterious facility by unknown forces is largely being pitched as a horror movie, so the integration of its core characters into the reasonably cheery MCU appears unlikely.

There are Fox superheroes who could be seamlessly integrated, of course. Deadpool has often had an amusing man-crush on Spider-Man in the comics, and Marvel has even begun to borrow the zany, meta-fuelled style of Tim Miller’s 2016 movie for its own entries. (Thor: Ragnarok is a case in point) Wolverine, with Hugh Jackman having finally hung up his adamantium claws, looks ripe for a Spidey-style reboot within the Marvel fold, and an MCU-led reinvention of the core X-Men (Professor X, Magneto, Jean Grey, Storm etc) would certainly be something to see. Yet what would happen to the actors playing these characters, currently stuck in the 1990s? James McAvoy and Michael Fassbender have occasionally done sterling work as Charles Xavier and Erik Lehnsherr respectively, but would presumably have to be aged up were they to suddenly turn up in the modern day MCU. Perhaps Doctor Strange could somehow pop back in time and rescue them from their current purgatory, some time after next year’s Dark Phoenix?

But what would happen to the superheroes who don’t fit snugly into the MCU? Would they continue to plough their own furrows? Would Disney-Fox simply draw a line under their big-screen adventures and reboot? This might be a pity, particularly in the case of offbeat curios such as Multiple Man and James Mangold’s mooted Logan spin-off about Dafne Keen’s X-23. Neither seems likely to survive a Disney-led cull, should it prove to be in the offing.

Marvel has its own problems to override as it approaches a second decade of the MCU. With Captain Marvel and Black Panther – both potentially totemic figures – due to get their own standalone movies in 2018 and 2019, it could be 2020 before the studio has the chance to begin integrating the X-Men into its wider world of superheroes. Feige has hinted he is not even certain that the universe will continue to exist in its current form, which suggests that the events of this year’s Avengers: Infinity War and its 2019 sequel could be so monumental as to throw doubt on everything Marvel has so far given us.

Does the studio really need the added complication of being forced to add the X-Men into the mix? On the other hand, might integrating Marvel Comics’ mutants prove to be the fresh injection of energy that the MCU needs to keep it thriving well into the 2020s?

One thing’s for sure, Feige and his team can’t afford to start making major blunders this late in the game. The future of the world might not be at stake, as it usually is when Tony Stark and his pals drop the baton, but the future of the Marvel Cinematic Universe certainly could be.