Oropeza, who was elected in 2006 and chaired the Senate majority caucus, was successfully treated for liver cancer in 2004, but fell ill again earlier this year.
She died Wednesday night of complications from a blood clot she developed in her abdomen in May. The clot led to a common side effect: a buildup of fluid in her lungs that affected her breathing.
The illness forced her to miss most of this year's session, including the vital votes earlier this month as the state passed a budget after a record 100-day delay.
Oropeza's name will remain on the Nov. 2 ballot. According to the secretary of state's office, she will be declared the winner if she receives a majority of the vote, and a special election would be called to fill the vacancy.