I have a catastrophic failure of my heater system too. In fact, I have seen two... one is my personal vehicle and one is a company car.
On mine, the heater pump (coolant fluid/heat pump compressor motor) quit, and after paying $1400 to have it replaced, it still doesn't work because apparently it leaked coolant onto the next part, which is a blower fan signal amplifier. Once that gets fixed ($700 or so), I'll find out if the PTC heater is blown (which I know from experience with the one at work is about $6-7 grand to fix, which was graciously handled by Nissan Canada).
I have been a big fan of Nissan and my 2012 Leaf, but this is brutal, even if it is marginally out of warranty. I certainly hope they come to the table to fix this situation if a simple heater fix looks like an $8k problem!