Yup, the coolant loss and overheating is what caused the head gasket issue. I hope the cylinder head is OK but again, that would be covered by warranty. The heater issue would be directly related.Yes, but not at first. The first problem was the heater wasn't working properly. Then the engine started stuttering. Check engine light eventually come on after the first few times it stuttered. Found there was NO engine coolant so filled it up, drove around the block and it was below min. again. Repeated that a few times as it wasn't holding coolant and eventually the over temp light came on. Wasn't holding coolant while running but was when it wasn't being driven (i.e. no leaks on the driveway). Couldn't drive it after that. That over temp light would go on when you started the engine cold. Had it towed to dealer last week.
The overheating was caused by the heat exchanger in the catalytic converter and that is where your coolant was going.
If the dealer does not replace that expensive catalytic converter with heat exchanger integrated in it, your issue will not be solved.
Several people on this forum have bypassed the heat exchanger with excellent results - quick and very inexpensive repair.