Scott's fate may actually depend on an element from an entirely different movie: the Soul Stone from Avengers: Infinity War. This gem has the power to control life and death by capturing a person's essence and storing it in the Soul Realm, which exists inside the gem itself. The souls absorbed by the stone remain trapped, unless the owner decides to set them free. In addition, the stone's owner can enter that world at will. We see Thanos do this when he enters an orange-hued landscape after snapping half the world's population out of existence.
With that in mind, we can conclude the Soul Stone contains an alternate universe or dimension and everyone who turns to ashes — including Dr. Pym, Hope, and Janet — is probably alive in the Soul Realm. And if that's the case, it's possible the Quantum Realm, with all of its time vortexes and anomalies, may contain a path to that alternate world. Ant-Man could use such a connection to establish contact with the Avengers who disappeared in Infinity War. Granted, in this scenario, Scott would still be separated from reality, but he would have a chance of escape should the soul for a soul theory that's been floating around the internet proves accurate or if Thanos returns to the Soul Realm where Scott could engage the purple beast in battle.
