What does survive mean? Are they going to keep on making movies? Yes. Are the movies going to be popular? Yes. Is the MCU going to be cultural phenomenon always ? Things fall out of extreme popularity see America Idol, Walking Dead, The entire sport of Horse Racing or Boxing,etc but even when something stop being extremely popular, It will be very popular aka Star Wars and previous mention Walking Dead both of those things are clearly not as popular as before but they are more popular than most things. I think that answer where the OP was going with the question.
Now let start with the other part of this the original Avengers weren't that popular to begin with none of them represent marvel "cool" heroes so to speak. They are recognizable and have level of popularity but they aren't what Superman,Batman,Wonder Woman and Spiderman are Now they became Iconic thanks the MCU run but we are talking about middle tier characters in terms of known comic book characters. This equivalent of me asking right now how is the DCEU going to survive without Flash,Green Lantern, Green Arrow,Black Lighting and Aquaman. And before someone says Aquaman made a 1 billion dollars understand he was in the same exact place as Cap,Iron Man,Thor,Black Widow pre MCU. The people who people feel are so essential were built into that and it was not preexisting thing.
The big point is movies both Marvel and DC have for general public move certain characters from relatively popular to bonifide stars. It did for the first generation characters like Iron Man and company and we have seen already work Black Panther and Captain Marvel. Marvel has already enough firepower to keep the wave going for awhile and if for some reason those guys keep the general public then Marvel has the plan B of Spiderman, Hulk, Wolverine, Storm, Punisher, Daredevil, Mr Fantastic, Thing, Deadpool, Blade aka Characters some of who are arguably more popular than Avengers characters being phased out. MCU will be okay