How to write about something in the future where something will have happened

Question

How could I write about something in the future where something will have happened? That is, I'm writing from the perspective of the current time, about a perspective in the future where something has happened between the two perspectives.

My specific case right now is to get the equivalent of "If you are reading this, I will already be dead" in Japanese.
Currently I'm thinking of 「これを読んでいるなら、私はもう死んでいました」, but that seems to translate more to "If you are reading this, I am already dead", that is, the perspective for it is in the future, but I want to write in the present.

• "If you are reading this, I will already be dead" ⟵ this
• "If you are reading this, I am already dead" ⟵ not this

Since this is a bit hard to understand, here's a drawing to explain what I want to do:

Time ───────────────┬────────────────────┬────────────────┬─────────────>
        Now (Writing the letter)       I die        Letter is read
                    └────────────────┐   └────────────────│────────────────┐
                       Writing from here, talking about this, referencing this event

@YangMuye suggested turning it into a question: 「あなたがこれを読んでいるなら、私はもう死んでいるでしょう。」Would this be the best way to do it?

While also helping me with my specific case, please also give a general answer to the question in case people need to apply it to other sentences such as, "In the future, androids will have been created", or "At the heat death of the universe, all black holes will have evaporated" (Yes, I'm bad at examples)

Answer 1

If you're sure you'll die and I'll read your letter after your death, then you'd say:

あなたがこの手紙を読むころには、私はもう死んでいるでしょう。
あなたがこの手紙を読んでいるころには、私はもう死んでいるでしょう。
(Literally: I will already be dead when you read this letter.)

If I won't read your letter if you survive, then you'd say:

あなたがこの手紙を読んでいるということは、私はもう死んでいるということでしょう。
あなたがこの手紙を読んでいるということは、私はもう死んでいるのでしょう。
(Literally: If you're reading this letter, then it means that I'm already dead.)

If you're not sure that I'll read your letter, but you're sure that it'll be only after your death that I can read it, then:

あなたがこの手紙を読んでいるなら、それは私が(もう)死んだあとでしょう。
あなたがこの手紙を読むとすれば、それは私の死んだあとでしょう。
(Literally: If you read this letter, it will be after my death.)

(Sorry if I'm misreading your question.)

Answer 2

Temporal sequencing in Japanese is quite complicated so to answer your question I am going to simplify the sentence, if I may, to:

If you have received this letter then I have (already) been killed in the war.

(This allows me to avoid questions about the use of 〜ている and resultant state verbs which is also complicated and not the main point of your question. It is covered in other questions on this site.)

The た-form indicates that an action has been completed not that it took place in the past. If you use なら then the action becomes hypothetical in the sense that it may or may not happen, or have happend, which is the situation when the letter was written but not when the reader receives the letter. The important point is that in your scenario, if the first statement has come true then the second statement will also be true. The sentence would then be:

この手紙をもらったのなら、私は戦争で殺されたのです。

If you want to add "already" then もう can be inserted after 私は.

Needless to say, when making such a statement the context has to be clear for the reader to infer the correct meaning. And, as you can see from Chocolate's excellent answer, the exact wording will depend on what exactly you want to say but if you want to know how to make a simple statement about two future dependent hypothetical events then I think this is one model that should work.