Well that's the beauty of the show vs the comic, nothing is set in stone. The show is not a cinematic version of the comic. If kirkman decides michonne is going to die, AMC could still do multiple seasons with her in them and even more if they decide they don't want to go with the comic exactly.
I personally think that michonnes death is not the end of the comic or show, in fact, it gives you someone to root for to not die in the show and makes me curious to see how the group handles without a key player.