Wintergirls: Deep Question

In the book Wintergirls, Lia is tortured by the fact that she did not answer the phone when Cassie called her, (33 times).  It is obvious that Lia feels guilty about not being there for her friend, when she needed her most. Do you feel that Cassie would have lived if Lia had answered her call? Also, have you ever felt that you have let someone close to you down when they needed you most?