Can cardioversion result in death?

Yes. There are complications of cardioversion such as stroke or rhythm problems that rarely could result in death.
Extremely rare. Cardioversion is a procedure where your heart electrical system is 'restarted', so technically your heart stops for a second or two. In elective cases, in extremely rare situations, the heart doesn't restart and the person dies. I would put the risk to less than 1 in 10, 000. In emergency situations, if the person is very sick, the chances are higher due to the overall comorbidities.