unlikely that it is headgasket leak? or unlikely that it isnt?Unlikely, you can do radiator leak down test to verify. You mostly can see the external coolant leaks and smell them.
Oh its an head gasket or cracked head for sure. The head gasket leak can be verified with the leak down test. The white fog and sweet smell on cold startup is a dead give away. Wither its the head cracked or the gasket at this point is irreverent. Another way to check is to take out the plugs and use an inspection camera to see the coolant coming into the cylinder.unlikely that it is headgasket leak? or unlikely that it isnt?