The #1 issue i have with no character death is simply that the idea breaks my sense of verisimilitude. You need to be able to die sometimes, because sometimes bad things happen and you're not going to make it. If that can't happen, the world ceases to feel real to me, and THAT'S why none of the other stuff in the game matters to me anymore. Because you're no longer a person in the world who might have a really bad day or make a big mistake and buy the farm. You're a protagonist with infinite plot armor, whose special story must go on. I'm not telling a story first, I'm a person in a fantasy world first.
Why does the lack of random, permanent, irrevocable death create, as you say, "infinite plot armor"? That implies a level of
indestructibility and guaranteed success which is not present, at least, not in my game; it very very strongly connotes that you see every attempted action as instantly successful with no real effort put in, which is likewise not true at all of my game or most no-death/low-death games (again, noting mine is technically the latter.)
I expect players to work with me and exercise good judgment. Being a ridiculous murderhobo who exploits genre conventions, flaunts logic, and dives headlong into danger "because the DM won't kill me, he said so!" will result in dead characters, because I won't tolerate that kind of behavior at my table. Being reckless because you have done the work to show your character has poor impulse control and a thirst for danger? Sure, knock yourself out (perhaps literally), so long as you aren't being exploitative. But if you cross that line into exploiting my goodwill, you will find I am not nearly so accommodating.
I, by intent, run a very magical world. It is also very mundane, which despite many claims otherwise is not a contradiction, because I work to include the lives of ordinary people and the ways magic can serve small domestic purposes (e.g., someone gained full financial independence and an income she could retire on via developing self-heating crockery, a crazy useful tool in the semi-arid to full desert Tarrakhuna region.) A world where the boundaries of life and death are fuzzy: the Spirit World exists, a layer of the mortal world that one must be trained to look into, where restless souls linger before passing on. As a result, resurrection is often (but not always) possible, and there are strange forces and unknown magics out in the desert, forgotten secrets and alien technologies which might permit things heretofore considered impossible.
That freedom to act comes with the great responsibility to use it very carefully. To justify what I do and why, in a way that is intuitive and reasonable but not so blindingly obvious that you can just see it instantly (well, not every time anyway!) Or, failing that, to make a quest of it: why IS this seemingly-impossible situation happening? We explore these results together. If a character dies, Death may make his bargain to restore them (a default thing in DW). Or the detested fiendish heritage of the character could rear its "ugly" head (actually quite handsome, for a half-devil/half-demon) and cling to life, but with Consequences for the character, e.g. "Oh,
you died, young Prince. But you remember how your...condition...was one where you were half-human, half-devil, half-demon? I'm afraid it was life finally balancing the scales...because your human half is what died. You are now a full outsider, just with certain
grandfathered-in perks, shall we say." Or a chorus of voices, those who depend on the PC as the last of their kind that can free them from their self-imposed exile, expend part of their own existence to preserve him, for without him they are lost.
Etc. These are not, at least to my mind, "plot armor." They are not bad consequences being wished away because such cannot be borne. Instead, it is something valuable to the PC being lost forever (unlike fiendish power, humanity cannot be simply obtained with the right kind of pact!), or a terrible price extracted from those the party desperately wishes to save, or the world itself bearing the scars of failure and defeat to forever remind the player "sure,
you lived, but at what cost?"
Incidentally, while I allow raise dead and similar effects in my games, it is much harder to accomplish at my table, and I personally never do it for my own PCs. Dead is dead if I have my way. That way, every PC's story has a beginning, and an end, and that mortality makes it worthwhile.
So, ends other than death simply do not exist? That's an unusually strong claim to make.
That said though, if what you want is for your character to stay dead if they die, awesome, you fit in perfectly. Because that means every time your character dies it has your active approval. I won't hold your fellows to that standard, but I can respect it as the standard for your stuff. That might make it harder to produce a narrative you would find engaging, but there are paths that can be taken--perhaps your character's story is more the story of a mantle he or she bears, similar to the Green Lantern rings or Captain America and his shield, where the death of one bearer does not totally snip the threads, but does significantly affect things nonetheless?