Jean and Scott quit the team so Scott can recover from having had a bomb put in his heart.
Seems reasonable.
#71 is a quiet issue, with Jean visiting with team-mates and saying goodbye. During issue #71, the X-Men learn that the Heroes Return(ed), and aren’t dead. Seeds are planted for more Apocalypse stuff (ugh–too soon). We learn that Maggot might be going around killing homeless people for some reason.
Most important, Wolverine tells Scott that things will be different after he leaves, and confronts Marrow about her bad attitude.
The two of them seem to have similar communication styles.
They fight for several pages until Wolverine goes feral and Cannonball breaks it up.
After the fight, Marrow runs away to find Callisto.
Meanwhile, Magneto–the real one–has returned, and Sabra is tracking him down. We learn that Erik Lensherr was never his real name when Magneto kills the guy who created that false identity.