Board Thread:Legitimate Canon Questions/@comment-41.63.165.91-20140626132336/@comment-77.3.74.228-20140626192921

Of course they could have let Allison live and still write her out (like Jackson and Isaac). BUT:

1) It would have been totally unrealistic that Allison just leaves her friends.

2) They wanted to keep Chris in the show. And he wouldn't have let his daughter leave Beacon Hills alone / alone with a werewolf (Isaac).