Has the retina screen effectively made dead pixels moot?
You will still be able to see the defect.

What retina means is that once two items with similar contrast get close enough together, you can't tell them apart - it appears to be one item.

Along a line, for instance, you can't tell where each pixel that makes the line is, but you can clearly see the edge created by the line on the contrasting background.

A dead pixel creates a contrast you'll be able to see.  If you have two dead pixels next to each other, you might think you only have one.  But you will be able to see them if the pixels surrounding them contrast.