At the end of his speech, the Architect explicitly states that Trinity is going to die and there is nothing Neo can do to prevent this.
The door to your right leads to the Source, and the salvation of Zion. The door to the left leads back to the Matrix, to her, and to the end of your species. As you adequately put, the problem is choice. But we already know what you're going to do, don't we? Already I can see the chain reaction, the chemical precursors that signal the onset of emotion, designed specifically to overwhelm logic, and reason. An emotion that is already blinding you from the simple, and obvious truth: she is going to die, and there is nothing that you can do to stop it.
Even though Neo saves Trinity at that instant, she dies only the next day, and Neo returns to the Source and to the salvation of Zion. The only difference is that Neo rejected choosing 16 females and 7 males to construct a new Zion.
The Architect has full knowledge of everything that is going to happen within the Matrix. His knowledge includes emotions as well, in spite of his inability to understand them. Thus, there is no way he cannot know Neo is going to save Trinity, yet he still states she is going to die.
One assumption might be him bluffing to goad Neo to go to the Source, however, he also states he is incapable of lies and deceptions as well.
I have your word?
What do you think I am? Human?
So, my question is, how did the Architect know that Trinity will die outside the Matrix?