Or maybe not. I just pulled a die and under it is what can be best described as an IGA (insane grid array). Let's just say it looks like a ball pitch of zero, but still bga. Maybe .1mm. But yes, the failure mode seems to be die overheats, melts solder under it, and either just shorts the +.6v lines or if very unlucky shorts the 3.3v supply to power the die's housekeeping.
Fascinating.
So it's possible that "dead" dies are actually not dead at all, but the solder below them has just melted and shorted across the array?