Now the new iPad has a retina screen, does that mean we can't see dead pixels anymore?
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.
No, you can still see dead pixels perfectly well - if you go close enough.
Actually, I received two new iPads - both with a few dead pixels (always black).
It was in both cases a patch of dead pixels, for one device I estimate around 4-6 and for the other 2-3; the patches were in different locations.
As the pixels are now so small, dead pixels are far less disturbing - nevertheless, I sent back both iPads because of that.