one can’t choose but wait

I lost my sister about ten year ago. I was young then. I didn’t really know what losing someone really meant. Instead, I was proud that I didn’t shed a tear when I heard the news or when she was cremated without my knowledge.
She was 23 when she died of blood cancer. Back then, I didn’t know what blood cancer was but I knew it was a painful disease that gradually kills.
A year passed after she was diagnosed of cancer. She was admitted at the Thimphu Hospital. She lay bed-ridden for months. Later she was referred to Vellore in India for treatment. Even after desperate attempts by doctors, they failed to get hold of a matching bone marrow.
She had never been the same after that. She loved to drink bottled Miranda juice, and despite her pain, she always had something funny to say.
A bunch of her front hair was grey. It was unique. High fever consumed her, her body too fragile to even sit upright and her face was dark because of the continuous blood transfusion she had to undergo.
Whenever I hear of a cancer patient, her poor fragile body and the pain comes back as if it just happened yesterday.
Recently, a friend of mine said she would not mind dying of cancer. She reasoned that if she knew she had cancer she would have the time to do good things, like praying and earning spiritual merits.
Does it work that way? What happens to those who die a sudden death? Do they not go to heaven? Everything has its own time. Some people are very religious at a very young age while some wait till they are a little older or old enough to start praying.
I don’t really subscribe to her ideas but perhaps this is why many people prefer dying while asleep.