You only have to complete the origin story without the main character dying in battle, not the whole game. If the main character dies in battle but the other characters survive you won't receive the achievement but if your entire party is killed and you reload your save it won't count as the main character dying.
Yes my english skills are terrible, lets all just pretend it's not my native language.
Michael is referring to the online achievement, not the actual XBOX one. I have gotten that one myself so I can personally confirm the achievement does NOT take saves into account. If you reload your last save any time your Warden dies then you should be fine. Its not that hard on Casual. Just always keep an eye on your character's health, as Blood Mages and the like can take you by surprise sometimes.