Lethal Weapon showrunner Matt Miller recently explained what was really going on when Wayans threatened to quit; the Season 3 finale indicates that Wayans will be as much of a part of the show in Season 4 as ever, assuming Season 4 happens.
The very good news for fans of Lethal Weapon as it is now is that the finale twist didn’t involve Murtaugh being written out, and there’s no sign that Damon Wayans’ earlier statement that he intended to depart the show after Season 3 still holds true.