It may be indelicate to make this argument just as thousands of fantasy fans are converging on San Diego for the annual Comic-Con. But the movie business may soon find itself mourning “the death of superheroes,” Susquehanna Financial Group’s Vasily Karasyov says in an intriguing report this morning. The analyst says that the boom in superhero movies began around 2000 as computer generated imagery (CGI) made it easier for filmmakers to credibly show action that defies the laws of physics. Virtually all of the most popular films of the last decade couldn’t have been made without CGI. Within that group Karasyov counts 16 superhero films, not counting sequels, resulting in four franchises: Fox’s X-Men, Sony’s Spider-Man, Warner Bros’ Batman, and Paramount’s Iron Man. Yet nothing has taken off since Iron Man came out in 2008, he says, largely because studios have already tapped their hottest properties. “As film studios dig deeper into catalogues for characters for new films, we think the chances of finding a break out property are diminishing fast” — even though the films still come with high production costs — Karasyov writes. If superhero films fail to catch on, then studios can forget about raking in lots of additional revenue from licensed merchandise. The bottom line: Investors should expect “growing risks to (financial growth) estimates” for companies including Disney and Time Warner that are looking to superheroes to help rescue their studio profits. And Disney CEO Bob Iger may end up regretting his decision to pay $4B for Marvel in 2009: Disney made that deal at “the top of the (comic book) character remonetization cycle,” Karasyov says.