Whenever I think about these things, I just think of the UK and how long they've been around. Wars, plagues, economic meltdowns, etc. They may not be the global power anymore, but on the whole, things seem to be working out fairly well for them. For the rest of developed countries, I don't worry much either.

The only countries I do actually worry about are China and russia, since both have lost generations of people either to capital flight, or self-imposed policies that have erased generations of young people and women. There's no way to undo that generational damage, even if you started importing immigrants 24/7 to get married and all that. Generally, big upsets like that result in massive wars/starvation/mass purges/etc.

That said, if I were Germany, I'd be working to get off LNG as soon as possible. I'd be looking at advanced nuclear and securing non-russian nuclear fuels in case climate change causes the ocean currents to shift and make things hotter/cooler around the north Atlantic and North Sea. Nothing good can come from russian LNG at this point. Investing in R&D in renewables, scientific advancements, and clean energy is probably where I'd be retrenching my economy.