One struggle I've had as a GM is the pressure of building thrilling, challenging encounters that aren't too over-tuned that they risk TPKs at every turn. Invariably, it happens, and my campaign comes to a screeching halt. This isn't just "the occasional TPK" or "they made bad decisions." This is literally every campaign I've run since around the year 2000. Even my first Level Up campaign stumbled before the characters could reach 3rd level.
I don't fudge dice rolls and I roll in the open so it's hard to keep characters alive in standard d20 games without having every enemy take prisoners; making suboptimal tactical decisions to favor the players; running easy and boring fights.
Not a one of those looks like pointless death, so I don't understand the question.
If the players are
chosing to enter into a challenge and wager the stakes of lethal combat, it is impossible for that death to be pointless. Not a opinion, that's the stakes the players are wagering, it by definition has a point. They are putting that forth as their wager. They don't have to -- they can run, they can negotiate, they can bypass, they can change strategies mid-challenge potentially.
So everything you suggested is robbing player agency. It's saying that even if they choose to wager their character's lives for the chance to overcome this challenge, you won't force them to pay. Making the wager worthless, the tension gone, and frankly them
more likely to make the wager when it will result in their death because they know there are no repercussions.
To avoid
meaningless death, make sure that as a GM if you force a challenge with battle-to-the-death as stakes, cutting player choice (including doing things like entering a dangerous dungeon) out of it, then make sure there are other end conditions available for the challenge, even if it's just a reasonable chance to escape.