How should I understand 〜ぬ時は?

Question

I'm confused on this picture. The question is, my teacher told me that

来ない時は(約束した日時または時間)

分かっておるであろうな(あなたはどうなるのか分かっているはずだ)

But I don't understand how can it change into this? I understand about the translated version from my teacher now but when I was trying on translation on the first time it went like this.

"The time that you doesn't come, You're understand?" It's weird right?

But from my teacher, I can understand it now.

Except I don't know how to change 来ぬ時間 into　約束した時間.

Is it some kind of grammar?

Especially 分かっておるであろうな into あなたはどうなるのか分かっているはずだ

I can understand that わかっておる can translate into わかっている but It's followed by であろうな.

What does it mean, and how can it turn into あなたはどうなるのか分かっているはずだ?

Answer 1

It's a good question. :)

来ない時は(約束した日時または時間)
分かっておるであろうな(あなたはどうなるのか分かっているはずだ)

来ない時は is actually equivalent to a condition/premise; もし来なければどうなるか. どうなるか is only implied, and continues to the question, 分かっているだろうな, which is to remind (you) what follows if (you) don't come, saying it in an intimidating tone like an old sage.

Answer 2

It literally says:

「来ぬ時は」 (≂ 来ない時は) -- "When you don't come / If you don't show up..."
「（どうなるか）分かっておるであろうな」 (≂ 分かっているだろうな) -- "I suppose you know (what will happen). / You know (what will happen), do you not?"

分かっておるであろうな, or 分かっているだろうな in modern/standard Japanese, is used as a threat here: "You see what happens?" i.e. "You better not!" -- "You should come! (or else...)" in this case.

The way the person speaks (来ぬ for 来ない, おるであろう for いるだろう) is the so-called 老人語 / old man's speech in fiction, a kind of 役割語 / role language in fiction.