Mia is our cello-playing, record-collecting, girlfriend-in-a-coma protagonist. Music is her life. Mia and her boyfriend, Adam, both love music and collect records. She has a promising music career ahead of her, because she has auditioned to the famed Juilliard School. And even though Mia often feels like an outsider in her own family, all her family members love music of some sort, and that brings them closer together. The fam that jams together, stays together.
Before the accident, Mia has a minor internal conflict related to the fact that that she doesn't think she fits into her family. The main reason Mia feels like an outsider is because her Mom, Dad, and younger brother have blonde hair, but Mia is a brunette. It's a hard-knock life.
Mia also tells us her that family is "cool." Her mom still dresses like a teenager. Dad wears sweater vests and smokes a pipe. Mia, on the other hand, thinks that she herself is a square because she plays the cello. But Adam, Mia's super cool boyfriend, tells Mia she is cool because she is herself, even with her brown hair. Well, that was easy to resolve.
As far as popular young adult protagonists go, Mia has the easiest life ever. Harry Potter was locked in a closet for years. Katniss Everdeen fights for her life over and over. Even Bella has to run from vampires. Mia's biggest problem in life could be solved by a box of Feria.
Mia is one of the "most promising students" (5.29) in her school. Each time she plays cello, it "sounded pretty amazing" (16.61). She has a hot boyfriend who would do anything for her. She has approximately two dozen people waiting for her to regain consciousness in the hospital waiting room. And she is so nice that she immediately forgives the man who killed her entire family, thinking that "his life has changed irrevocably too" (11.7).
Basically, girl's life is perfect except for that whole car-accident-killed-her-whole-family thing—a sobering reminder that bad things can happen to even the most charmed people. All the same, the accident doesn't seem to affect Mia too much.
You might even find it a little strange that Mia doesn't react more strongly to her family's deaths. Elizabeth Kubler-Ross outlines the seven stages of grief as shock, denial, anger, bargaining, guilt, depression, and acceptance. Sometimes shock and denial can be combined, and so can bargaining and guilt. Mia is either stuck in the shock stage, or she jumps straight to acceptance and hope because her life is so promising. There is never really any denial, anger, or depression in Mia's story. Maybe she just hasn't had enough time to process everything.
Now, you could argue that there is some bargaining in her choice of whether or not to live, which is Mia's only real conflict after the accident. But in this bargain, all the chips are on Mia's side of the table. She isn't spiritual, so for her, there is no afterlife. Her choice is between total darkness or living an incredibly charmed life, full of love and success. Why would she choose death?
Mia does have a difficult choice before the accident, in trying to decide between Adam and Juilliard. Here's Mom's advice: "Either way you win. And either way you lose" (15.82). Well, that's true, Mom, but that's also no help, at least as far as Mia can tell. But what Mom means is that there are different kinds of love. Mia loves music, and she loves Adam. They are different types of love, but each is equally valuable to Mia.
However, the book doesn't give us the payoff of seeing Mia's choice. Gayle Forman saves that for the sequel—although the fact that Mia returns to her body only she hears cello music playing should give you a hint as to what she will choose.
We'll quickly examine the meaning behind Mia's name before we finish. The name Mia can mean "loved one" or "bittersweet" (source), two meanings appropriate for this character. If Mia had nothing—if she lived in poverty, or had no other friends and family members, and no prospect of a successful future—her decision between life and death might be difficult. But as things actually are, Mia's fate is bittersweet. Her family may be dead, but she'll be just fine.