11 Ways Marvel Could Remedy That Insane Ant-Man Cliffhanger

Since the midcredits scene makes note that Scott enters the Quantum Realm to collect quantum healing particles for their new "friend" Ghost, we can safely assume she's alive but still suffering side effects from her condition. This implies that Dr. Foster and Ghost are nearby and don't flee the city as the conclusion of Ant-Man and the Wasp would suggest. So perhaps Ghost uses her phasing ability, and the quantum energy given to her by Janet near the end of the film, to help locate Scott while Dr. Foster brings our hero back using the research techniques he once shared with Dr. Pym or his old connections at S.H.I.E.L.D where Ghost had once been a high-level assassin.