Did Clarrise die? If so, how did it happen?

We aren't given definitive information, but Mildred tells Montag that Clarisse was hit by a car. She also mentions that the family has moved away.

"No. The same girl. McClellan. McClellan, Run over by a car. Four days ago. I'm not sure. But I think she's dead. The family moved out anyway. I don't know. But I think she's dead."