Those are two separate agreements, and to play a game in which character death is not a possibility does not mean that the heroes always succeed (whatever succeed means in this context). I mention this because it's not clear that you are making a distinction between the two.Take two groups and run them through an adventure. The first is a group that agrees on no character death ever and the heroes always succeed.
I wouldn't say that either group really accomplished anything other than to play a game that I hope they enjoyed.The second in my game: hard core hard fun unfair unbalanced anyone can die at the drop of a die anytime. When the first group successfully completes the adventure did they really accomplish anything? they just sort of automatically succeeded as that is the game they played. My players had the hardest time possible and really had to make a huge effort to succeed. It makes for a very different game.