Can sight be lost from a stroke, and then regained?

This is a bit of a complex situation, but I'll try my best to give you some answers.

First, I would agree with the Neurologist you saw. Your fiance's See also:
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See all 502 questions about Stroke vision problems are not due to a standard "stroke", and therefore an Ophthomologist or Neuro-Ophthomologist would probably be better at giving you answers as to the recovery that would be expected.

A standard "stroke" would be expected to cause a blockage of the artery that supplies either the eye itself or the parts of the brain that control vision. This is not what happened here. My guess is that your fiance had a clot in the veins behind the eyes, which caused a build-up of pressure behind the eyes, and thereby damaged the eyes. This is different than damage resulting from an occlusion of arterial flow to the brain or eyes.

In general, the brain and eyes can recover after damage has been done, but they typically do so at a slower rate than other organs. Also, often recovery is not complete.

Given his improvement thus far - now seeing outlines of shapes - and the information about the left eye having no visible damage, I think there is reason to hope for further recovery. As a general rule of thumb, recovery continues for anywhere between 6-24 months after an injury, but I have heard of recovery even farther out. This website is full of stories from people who have continued to have some recovery long after the standard 24 month window.

Given the complexity of the situation, I very much agree with the advice to see a Neuro-Ophthomologist. And I certainly hope your fiance the best of luck with continued recovery of vision.

I wanted to add that he is 33 years old.