Mark Waid's 12-issue run on Action Comics just came to a close, and with it Mon-El's story.
Spoilers for those that didn't read it, but want a quick summary of the end:
The Phantom Zone has now been returned to its old state which most Legion readers will be familiar with, that of a void with little physical matter, and both Aethyr and Xa-Du have been removed from power. Mon-El is now the Warden of the Phantom Zone, deciding if the various "zoners" imprisoned there have truly repented and are worthy of being freed into the material plane. If so, they are freed from the zone by the Kandorians and live in the bottled city. Mon-El got this position because the Kandorians observed his actions in the previous issues and decided he was the one they trusted most.