I was intrigued to know that there were actually fans of Smallville that deeply love Chloe and were hoping that she would stay on the show and have a relationship with Oliver and close out the show. Now we know that Smallville has been renewed for a 10th season, but at the moment, there is no word on whether or not Allison Mac will reprise the role of Chloe Sullivan, a character not based from anyone in the comic books, but has been on the show since the very first episode of Smallville.
Last year, Allison made a comment about Smallville, it's future, and her plans to move on with indieWire Blog Network.
Matt: What’s the latest with Smallville? How do you like living in Vancouver?
Mack: The latest with Smallville is that we have another season [after this season’s finale on May 14]. Tom has signed for two more, so the show will go until season 10. I will be completed with my contract next year, and I am looking for new and exciting ways to carry out my character’s exit. I love living in Vancouver, it is one of the most beautiful cities in the world. I love the people, the food, the aesthetic, and the life I have built here. It’s wonderful.
http://blogs.indiewire.com/mattdentler/archives/2009/05/11/five_questions_for_allison_mack
So she's said it herself. There has always been a possibility that Chloe will die, but we've been waiting for that for a very long time now. It's been foreshadowed that Chloe could possibly go insane, and Allison even mentioned that it very well could be a connection to her family history of mental illness and Dr. Fate stating that they were alike. Or, Chloe could simply decide to leave Smallville. It would be the least messiest way to tie up her story. No grief. No fuss. Just gone.