My understanding is that Europe has several months of gas reserves. Even if Russia cut it off completely, the real pain would come next winter rather than immediately.

Where do you store that much gas?

Underground:

https://en.wikipedia.org/wiki/Natural_gas_storage

This blows my mind! I knew you couldn't possibly store so much in tanks, but the idea to pump it into the ground is really insane.

Pressurized tanks, I assume.

Not really:

https://en.wikipedia.org/wiki/Natural_gas_storage

Thanks. Funny thing is I even knew that at one point, but had forgotten. At least I included "I assume" in my comment rather than stating my faulty assumption as fact!

I'd say late in winter could be really good for that strategy, depending on the weather. Doesn't explain this fully tho, more the opposite, so probably other factors played a larger role.

I read a few days ago that Germany's gas reserves were at 31% and they were basically just being helped by the good weather. A colder winter would've made it a much bigger problem. And Germany had very recently decided to basically go cold turkey on nuclear, which means using more gas plants. Now they're thinking of extending the life span of nuclear a bit. Not that a gas furnace can heat with electricity though, so not sure how much that will help.

Would probably be enough for the next winter as well, so not reason to panic. Then you still have the expensive option to heat with electricity or the cheap one to heat with wood. Warm water would probably be the largest problem, but that is far away.

I don't think it's a question of being expensive, but more like completely impossible. One good thing is that heating in Germany usually is via radiators that are water fed and the water is heated "centrally". Even in single family homes. Apartment blocks have different options. Some are central (basement heater feeding the radiators) but also some apartments have a gas heater in every apartment individually feeding just that apartment's radiators and gas is distributed throughout the apartment block.

If you had to replace every single gas heating system that would be both very expensive and without having any actual data I would gather that you wouldn't be able to retrofit all of Germany with that in time. Wood I would gather is gonna be even worse. While I can see how a single family home would convert (lots of folks have replaced their gar furnace with a wood pellet heater w/ auto-feeders), how would that work for apartment buildings with individual gas heaters in the apartments? These are all concrete buildings where it'd be quite the feat to replace the gas distribution with central water distribution for radiators. And those gas heaters do not take a lot of space and are used even in tiny apartments. Where do you store wood pellets in that situation?

Of course there are exceptions where heat is provided remotely already by a "Heizkraftwerk" (e.g. fed from industrial cooling systems or garbage burners).