"You break it, you die."
The English sentence is odd. It's clearly not simply two statements, but really an "if...then" type of statement. Klingon tends to be more clear on this kind of relationship and -chugh is definitely required. This sentence was included as an exercise in learning how to recognize when the Klingon needs to be different from the English.
Marc Okrand's Klingon has several of these examples of "THIS! or THAT!" being translated as "if THIS then THAT." This Duolingo sentence is simply copying that pattern.
bIjeghbe'chugh vaj bIHegh Literally this is If you do not surrender, then you will die, but Okrand translates it Surrender or die!
bIje'be'chugh vaj bIHegh Literally, this is If you do not buy, then you will die. But Okrand translates it as Buy or die!
There is nothing wrong with translating these English phrases literally: yIjegh pagh yIHegh; yIje' pagh yIHegh.