And at the same time highly implausible.
Fine for a movie, but not what I really want from a character in a D&D setting. That said, D&D characters come equipped with these things called hit points, which tend to serve largely the same function to a certain - but limited - degree.
This raises a valid point: in a less-violent type of game - e.g. one largely based around courtly intrigue where any actual fighting is done by NPC armies and mercenaries - then character death need not be much if any of a factor; as you're not out to kill your courtly foes, nor are they out to kill you.
But if you're out slaying monsters, it's only fair the monsters have a chance to kill in return.
In broader terms, the PCs can expect to get back what they give out.
A rotating cast can and does still has a narrative, though: that of the party as a whole rather than of any one individual character. That's the difference: characters can come and go all the time but as long as the party continues, so does the narrative around it. Same as a sports franchise - nobody who plays for the New York Yankees today played for them in 1982, but it's still the same team and people who aren't me still cheer for it.