So today I was playing the Arena mission and at about level 17, I finally died. Much to my surprise though, I quickly got back up on my feet with full health. At first I thought I must have accidentally used a defibrillator or something, but no. Turns out every time I would die, the game would automatically resurrect me. I eventually got to level 25 before just quitting.
The problem of course is that none of your accomplishments get saved as you never finish the mission.