What is the syntax of ille in the sentence: "numquam est ille miser cui facile est mori"? I get that cui is indirect object, but what is the function of the demonstrative pronoun ille in the sentence?
In this case, ille is the subject of the sentence: just generically "he", or "that man", or "that person" (since masculine gender is sort of a default in Latin), or even just "the one".
You can split this sentence in half to make translation easier. The first half, numqvam est ille miser, is a full sentence in and of itself: "that man is never miserable".
And who is "that man"? That's what the second half clarifies: …cui facile est mori "…for whom dying is easy". To make this a bit more idiomatic in English, I'd say "someone who can die easily is never miserable".