I am not very far into this game. I have not come across any items that prevent insta-deaths from normal play.
When I go from floor 1 to floor 9 out of 10 floors total, and then get one-shotted by a low level monster out of sheer luck it ruins me. I take the game out as quickly as possible. I should not have to use an item to jump out of the dungeon, save, and then go back in due to fear of being cheated. If I could save anywhere, it wouldn't be such a big deal. If those pointless spells did not exist, it would be much better.
It's not like I ever want to test my luck for a one-shot, and the bosses are never vulnerable to it anyways. Why do they exist in terms of serving the game's overall feel, or making it more fun for me? I hate them.