I had a nightmare with this on the last screw last night. I broke three watchmaker screwdrivers trying to get the last long screw out of a 2012 Macbook pro. In the end the head was so badly stripped I decided to drill the head ..
In fact this was pretty straightforward in the end, as the head is flat and quite thin, so didn't need much drilling. I got the remaining thread out with small pliers as there was 3~4mm above the point it disappeared.
Just need to get a new screw now. I wonder if I can blag one from an Apple store?