Ant-Man will return... But aside potential sequels and cameos in upcoming MCU films, ideas introduced in the film might have a big impact on Marvel's phase. Beginning with the next Captain America: Civil War, the major question has to be: whose side will Ant-Man be on?
The movie already gave out some clues as to where Scott's Lang loyalty may lie; thanks to what seems like a budding friendship with Falcon which, like any superhero friendship, begin with a fight. In fact, the final scene revealed that Falcon was looking for Scott. The post credit scene shed more light on this as Captain America and Falcon discover an injured Bucky with an arm stuck in a vice. The heroes need help handling him, remarking that "it would have been easier" a week earlier - suggesting that something big happened. A Registration Act maybe? This sounds like the MCU equivalent of the Superhero Registration Act from the comics, it dictates that all super-powered humans register with the government must receive training before performing heroic duties.
Hope Van Dyne (Hank Pym's daughter) will be getting her own superhero identity as The Wasp and must be involved somehow in future movies, in solo or more likely as a supporting character.
Plus, Hope's mother was lost in the Quantum Realm but Scott entered this mysterious realm and more importantly returned - thanks to Hank Pym's enlarging disk. Pym spent years studying this realm in hopes of retrieving his wife. That event sparks his interest once again.
This realm opens a whole new frontier, a whole new dimension even as Scott was technically shrinking at a subatomic level. Where concepts of space and time are completely irrelevant. In comic book language that must mean a whole new universe to explore for our superheroes!