as long as you never hit an unlucky streak.
I run high power games (lots of items cool inate abilities PCs learn like magic items, higher stats) and I find my players hit way above there weight class (they should see above) but even still I have come close to TPK with 'easy' encounters if a player does something dumb or gets a string of bad rolls or if the monsters get good ones (god forbid all three happen that IS a TPK)
Unlucky streaks do happen. I have had that as a player and a GM. It makes for interesting gaming. People go on streaks IRL, so I find it emulative.
Not a problem.
I mean if I drop you to 0 and an AOE hits you, that also gives a auto failed death save...
I don't know if it is 100% RAI but as I understand RAW, if my multi attack opens with a crit, I drop you then I hit you again it is also a failed death save...
so 1,2,or 3 50/50 rolls later you can be dead... and at low level a fireball can kill you...
a 4th level wildmage rolling (not my story but I don't doubt it) the fireball effect and getting 8d6 and was at less then 20 hp so died out right...and the rogue was down in the AOE already having failed a death save... so he died outright and she died the next round.
my most resent PC death happened when I (wizard) and the Cleric were both making death saves... a party member stabilized the cleric figuring I only had 1 failure and 2 successes but I rolled a nat 1 and auto died.
I don't see the problem here.
These are all potential consequences of running the game as intended. It is what makes the in-game stakes lively and gives PC's real sense of accomplishment when they overcome challenges.
If the players say that they want to play 5e, but don't want the possibilities of PC death that you outlined above, then they really don't want to play 5e.
They want to play a game with a "D&D" veneer, but with a much different rules system.
A "death flag", as I've normally seen the term, is that the PC can't be killed (they can suffer and lose, but not die to a random roll) unless the player explicitly says the character is willing to die due to the importance of a particular scene, and gain benefits for the scene due to the risk.
Well, that is shifting things to a completely different gaming paradigm.
The die mechanic is now completely removed as a neutral randomizer to resolve in-game actions.
You can house rule a system - adjusting the dial up and down a few places to better tune in to what you want to do at the table. The optional rules in the 5e DMG do this.
But there is a
fundamental difference between a 'house rule' that adjusts system mechanics in a predictable fashion - and one that says: At this point
we ignore the mechanical system entirely, because 'story'.
Why fight the system (By introducing a 'rule' that short-circuits it entirely) if your play expectations differ so drastically from the intended play paradigm of the RPG you are using?
Why not use a game that incorporates these aspect from the get go?
A more purpose designed RPG where impromptu lethality is largely removed, or a straight up Storygame would far better serve the needs of the table if complete narrative control of in-game outcomes is desired by the gaming group.