Just had the same problem with my 2011 Leaf. The PTC heater has a high voltage (400V) control circuit on one side, and coolant on the other side. The seal had failed, so coolant got into the control circuit and short circuited the 400V connection. That blew a fuse in the DC/DC junction box (which distributes 400V from the battery to A/C compressor, heater, motor and charge port). Unfortunately, the fuse is not serviceable (not a standard type, not available from Nissan). So I bought a new heater and junction box from Nissan for $2350 and replaced them myself. Nissan quoted me $4300 for the job, which is not unreasonable. It's a big job, which should only be attempted by a fairly experienced home mechanic, who UNDERSTANDS THE SAFETY RISKS INVOLVED WITH HIGH VOLTAGE CIRCUITS.
So yes, if your heater doesn't work, you most likely need a new heater and DC/DC junction box, and it will be expensive