Before Scott enters the Quantum Realm, Janet warns him: "Don't get sucked into a time vortex. We won't be able to save you." The implication is that Scott could find himself drawn into a wormhole and potentially travel through time, space, and other dimensions. However, based on Janet's tone and Dr. Pym's previous warnings that time isn't always linear, we believe time vortexes in the Quantum Realm are difficult to control (think Quantum Leap) to the point where a clean escape may prove impossible — after all, Janet spends 30 years in the Quantum Realm and never successfully uses one (as far as we know).
Even still, the warning points toward a potential escape plan where Scott could travel back through time and discover a way to set things right through the people he meets along the way. In fact, if we think of the Quantum Realm as multidimensional (think Doc Brown's explanation of alternate time lines from Back to the Future 2), one of those people Scott could encounter is a younger Janet van Dyne. Together they could create an effective exit plan or use their quantum entanglement (i.e. psychic connection) to send out a message to those who've dabbled in quantum energy or to those who've traveled through time like, say, Captain Marvel or Doctor Strange.
