Is the empty spots going to be filled with hair or not? (photos)

If you see empty areas after surgery, it probably means there was no hairs transplanted in those areas.  This may be a normal thing to see but if you are concerned, it is best to go back and ask your doctor for a recheck.

To me it doesn't look like an empty spot. It's doubtful any HT doctor would just miss a line of scalp. What likely happened is that the skin contracted creating that fissure looking area. It's like cracks in a dry river bed. They are normal and represents the sum forces of the skin healing and contracting. These area are stretched out, but then return mostly to their normal state. You likely won't notice them near as much as you are now. This is common in high density transplants and usually mean absolutely nothing in the end. Don't stress. 

You should go back and speak with your doctor about missing areas. At the 4 day mark, what you see is what you got. When you see your doctor, he can assure you one way or the other about what you are observing.