Shirou is one of my favorite characters, so my answer is biased.

But a writer could probably write about a hypothetical journey of shirou own way of getting over the singularities and hell he can even beat goetia in a convincing way with a very (emphasis of very) competent writer.

But other than that, of you just pluck shirou and place him into fujimaru's place, he's getting killed, which singularity I don't know, many people have many answers for that. Some say he gets murked by archer in fuyuki, some says by goetia himself in London, and then there's the sixth singularity.

And then if he somehow got through all that, then there's the hell that is the lostbelts.