How is that fully accurate? It seems to me that "not very survivable" is not accurate and is an over exaggeration. I don't expect a 50% death rate, even 10% would be extremely generous. It would be like me saying linux desktops are very common.
I would not leave my house. My house has insulation and thermal mass, which would delay the tempature from reaching that level until later. I could use water to cool myself, whether in the bath tub or a trashcan. I could use a fan if there's power (depends on the temperature and humidity to reach that wet bulb). I could use frozen objects (even without power, the freezer will stay cold for at least a day). I also have a generator to power these things if there's a short to medium term outage.
Their statement was not about changing one's circumstance. It was that even with precautions, it's not very survivable. This is neither accurate nor precise. It is very survivable with precautions.