A stranded ICE vehicle will exhaust its gas tank in 8 hours, max. You can turn it on an off to stretch it out but I wonder if you'll just burn more gas that way. Google (and Quora) suggests that a Tesla will last 36-72 hours, "or less" if it's very cold. I think EVs win in this case, assuming a full tank versus a full charge.
Regardless if you're in a place where this could happen you should have a box of chemical handwarmers, a heavy blanket, food, water, and other stuff in a box for emergencies.
Edit: looks like I'm wrong, much better answers below!
Where are you getting the 8 hours from? A car that gets 30 mpg with a 14 gallon tank can _drive_ for nearly 8 hours at 60 mph. That same car may burn (on the highest end) 1/2 a gallon an hour idling which would be more than 24 hours of idling time.
> A stranded ICE vehicle will exhaust its gas tank in 8 hours, max. You can turn it on an off to stretch it out but I wonder if you'll just burn more gas that way.
A 4.2L engine burns 0.39gal/hr under no-load conditions according to the study there for a large sedan. Let's assume that the load of putting the blower and heater on equate to even 1 gal/hr (an absurdly high value, the rule of thumb I can find quoted in a few places tends to be add 10-20% depending on interior size and conditions outside).
Let's also assume a fuel tank size on the lower end (~15gal) for this sedan.
This means in the absolute worst case conditions (you're blasting maximum heat the entire time) around 15 hours of operation for a full tank, 7.5 if you had half a tank.
Comparatively, the Tesla, depending on Model, could use as much as 4.8kWh[0][1] under similar worst-case conditions. Modern versions of Tesla and other electrics have or are moving to heat pump heaters, which is encouraging as it will likely be better generally (though this comes with the caveat that they don't work as well in lower temperatures and I believe are supplemented by coil heaters under those conditions).
At any rate, the worst-case electric scenario gives a full-charge length of 18.75 (90kWh useable out of a 95kWh pack in the largest long-range models) or 9.38 at half. Note, this is giving the Tesla an enormous advantage here as I'm going with the largest battery pack possible. With the long range pack available in the Model 3 those numbers drop to basically the same as the smaller-tanked gasoline sedans.
If you have better sources for those numbers on the Tesla idling with the heaters on, these were all I could find quickly.
So in essence, if you're stuck for a day you're going to be screwed regardless, except for some edge cases like a large full tank and an ICE that doesn't consume a lot of fuel when idle, or a heat pump driven EV with a full charge in a decently sized pack.
There will always be older or less efficient cars, smaller gas tanks, smaller battery packs, resistive heaters, and people not rationing the energy available to them.
Rough metrics say idling can consume anywhere from 1/3 of a gallon to a gallon per hour of idle time.
Taking the worst case, and why not because it's cold, and people may be inclined to do more than idle their engine, means roughly an hour per gallon of fuel.
Some ICE cars may only idle for a few hours, others a lot more, depending on what's in the tank.
Best move is to pulse the engine. Start up, idle until the vehicle is really warm, shut down and repeat every other hour or so, depending on the cold and what people have to stay warm with.
Regardless if you're in a place where this could happen you should have a box of chemical handwarmers, a heavy blanket, food, water, and other stuff in a box for emergencies.
Edit: looks like I'm wrong, much better answers below!