I want a word that describes the "in real life" enactment of a metaphor/story/situation that occurs in a piece of literature.

Example: Robert Frost's famous "two roads diverged."

I want to construct a sentence that says, "Quite a XXX of the archetypal two roads."

Hi and welcome HNK.

Does not the simple form do it?

"Quite an example of the archetypal two roads."

- or exemplum if you want to be fancy and Latinate ;)

If this bus doesn't go where you want, there'll be another few along shortly.

exemplar
instantiation
instance

In slightly different circumstances, one might use
specimen
implementation
case in point

k

"Quite a life-imitating-art of the archetypal two roads."

This isn't a serious submission, of course, but it might spark some more ideas.

How about "embodiment"? Or "incarnation"?
And welcome to the world of wordies, HNK.

You are speaking, I take it, in this example, of a decision with life altering and irretrievable consequences and not of a fork in the road. I wonder why you would want such a word at all -- 'example,' 'instantiation,' etc., when the power of the metaphor, if it is worth its salt, and if it has been so established as the archtypal, best, or canonical expression that it is itself the best term. In that case, the metaphor weakened, in my mind, by the construction of your sentence, which only references, but does not employ, it. That construction would, however, function very well, if it were used in elision: the notion of example being suggested, but not actually stated. As a "grammatical" question, however, I think the question is interesting whether there a specific term for this. And I have no idea the answer.

Hmmmm, I was hoping there was a word I didn't know of that encapsulated the precise "literature to life" definition. That would be a fabulous word! Something more sexy and classic (possibly french?) sounding than "lit-to-life."

The term does not convey the full range of meaning but how about "tableau vivant," meaning a representation of some scene by means of persons grouped in the proper manner, placed in appropriate postures, and remaining silent and motionless. Think of Robert Altman's tableau vivant of da Vinci's Last Supper in the 1970 film adaptation of MASH.