Ant-Man and the Wasp

Scott volunteers to re-enter the quantum realm to harvest quantum energy needed to stabilize Janet's energy signature during the rescue attempt. While inside, he absorbs excess quantum energy, which causes him to become trapped when the extraction window closes unexpectedly. This trapping is accidental rather than intentional, setting up the circumstances that protect him from Thanos' snap.

Hope, Hank, and Janet Van Dyne disintegrate because Thanos has activated the Infinity Snap off-screen, erasing half of all life in the universe. This happens moments after Scott becomes trapped in the quantum realm. The timing creates a cruel coincidence: Janet is finally rescued only to be snapped away almost immediately, leaving Scott alone and unaware of what has happened.

Scott survives because the quantum realm exists outside normal spacetime and appears to be unaffected by Thanos' snap. While half the universe's population turns to dust on Earth, Scott remains trapped in the quantum dimension where the snap's effects do not reach. His survival is essentially luck, he happened to be in the one place the snap couldn't touch when it happened.

Janet Van Dyne is successfully rescued from the quantum realm after decades of being stranded there. However, her rescue is short-lived, she is snapped away by Thanos almost immediately after being reunited with her family. This creates the film's bittersweet ending, where the protagonists achieve their goal only to lose everything due to the Infinity War events.

Scott's five-year entrapment in the quantum realm becomes crucial to Endgame's time-travel plan. While trapped, Scott experiences time differently, what feels like hours to him turns out to be five years in the real world. This phenomenon, combined with his knowledge of the quantum realm, allows him to propose the Avengers' time-heist strategy to retrieve the Infinity Stones and reverse the snap.

The film's post-credit scene and the quantum realm's unique time properties hint at Scott's importance to the larger MCU.

Scott is the sole survivor because he was inside the quantum realm when Thanos executed the snap. The quantum realm exists as a separate dimension that operates outside normal universal boundaries, making it immune to Thanos' universal culling. His teammates, Hope, Hank, and Janet, were all outside the quantum realm when the snap occurred, leaving them vulnerable to its effects.

The post-credit scene shows Scott's pet ant hissing at a drum set in Scott's empty house, implying the ant has been left alone since Scott got trapped. The scene is played for humor, suggesting the ant somehow learned to play drums during Scott's absence, but it also underscores the loneliness and uncertainty of Scott's situation. The emptiness of the house foreshadows the snap's devastating effect on his loved ones.

Janet's quantum energy is crucial because she has been immersed in quantum realm energy for thirty years, causing her quantum state to become unstable. The team needs to harvest additional quantum energy from the realm to stabilize her and allow safe extraction. This is why Scott volunteers to return to the quantum realm, their original plan requires more energy than they initially calculated to complete Janet's rescue.

The film doesn't explicitly explain why Betty Brant (played by Judy Greer) isn't seen turning to dust, though she is Hank Pym's former colleague and could have been present. The snap occurs off-screen during the film's final moments, focusing only on Scott's team. Betty's fate is not addressed because the scene concentrates on Hank, Hope, and Janet's disintegration as the emotional core of the cliffhanger.