Rick kicks the bucket, with no one else to step in as leader, Michonne steps in, but she has no real leadership experience. There's only one other known leader living in Alexandria: Negan. She consults him for advice (much like Rick did in the comics). They eventually start to build rapport (over a LONG period of time), Negan begins to genuinely earn back the group's trust and either remains a co-leader with Michonne at Alexandria, or stays in the background as some sort of trusted advisor. Either way, he becomes an important member of Alexandria.
Now this complicates things with Maggie. Maggie wants to kill Negan to avenge Glenn's death, but also realizes this will start a war with Alexandria and the Hilltop. Tensions rise until the Whisperers' come along and they're forced to set things aside to deal with this threat.
Then at some point way later down the road, Maggie grows out of her blood feud with Negan.
except that wont happen because lauren cohen is basically leaving the show as well the comic took the maggie/negen relationship to an interesting angle she doesnt forgive him for what he did but realizes he feels genuine guilt for his actions so letting him live with his guilt is a worse fate than just killing him like he wants her to do so thats how she gets her revenge but letting him live ---