The main character cannot die in the first act.
I thought Darsteller was more like actor than “character”, unless this is specifically a play or some sorts, then wouldn’t a cleaner translation be more like “leading actor” instead of main character? I always though Germans use Hauptfigur for “main character” specificially?
Hey, probably no the person that you’d like to see replying, and yet here we are. I propose that we bury the hatchet and start anew, to keep progressing in the path of language learning.
Regarding the sentence; I am no German native by any means, but I had the same impression as you - I though “Darsteller” to mean actor and not *character". So I’ve been looking around, and the dictionaries seem to agree, both the wiktionnary and pons translate Darsteller as Actor. I’ve also looked into an english dictionary, in case there was some obscure meaning that refer to the actor rather than the character, but it doesn’t seem so either.
Looking at tatoeba, in case it was just a mistake corrected after Clozemaster’s extraction, the sentence seems to be as is. However, the user who translated the sentence, although a German native, seems to only describe themselves as “not bad” in English. So my best bet is that they interpreted “character” incorrectly when translating it to German.
So, unless some native German sees this and has something to say about it, I’d say that the best would be to report the sentence to Clozemaster so that it (hopefully) gets corrected for everyone, and, in the meantime, correct it for yourself directly
German native here.
The German sentence is probably a bit sloppy.
If the “Hauptdarsteller” (leading actor) really dies in the first act, he will never play again. 
Of course, this might tragically happen, but it’s rare.
If the “Hauptrolle” (main character) dies in the first act, the “Hauptdarsteller” can be on the stage again the next evening. 
That said, I would not be surprised to read the sentence as it is in a theater review in a newspaper.
So, if I understand what you are saying, “Hauptdarsteller” does really only refer the actor, and not the character, right?
Strictly, yes.
But I think that even many native speakers will not always consider this. So, it is nothing that a non-native has to worry about. Nobody will give you a strange look for it if you mix it up and context will always make clear what is really meant.