If he does leave for a bit they don't have to kill him.
For example, he could easily make an attempt on Negan's life, fail, then run away and hide so that nobody knows where he is. Come back in a year or two when the heat is off, aka studies have eased up.
Or he could decide to take Enid someplace safe and come back from the jaunt when time allows.
I don't think things would go well if Carl died as it would have to affect Ricks character in an extremely powerful way, perhaps beyond what the character strength of the show could endure.
However, we shall see...
Regards and Happy Thanksgiving,
Doug