The superhero bubble might burst one day, but then they'll move onto adapting non-superhero comic books. To this day, I'm convinced DC will make money hand over fist with '100 Bullets', 'Scalped', 'Y: The Last Man' and 'DMZ' films, but they haven't pulled the trigger yet.
Hell -I'd still love to see them do an animated Black and White version of 'Sentences' - MF Grimm's graphic novel autobiography, but they don't fukk with Vertigo, because a lot of the material is creator owned.
If it does crash - they'll just reboot them down the line. I talk to my 5 year old nephew about superheroes, that means there's a generation is growing up on these movies now. They'll trade on nostalgia next time around.