Re: Sanctions
Sanctions can work. Iran is negotiating over its nuclear program, because it wants access to Western finance and capital markets - and access to parts for its oil industry.
I think, in general, sanctions can work over countries that aren't total dictatorships. Russia isn't a true democracy, given there's little media freedom, most media is government controlled, people are barred from elections on political grounds, the courts are only partially independent etc. But there is limited freedom and democracy isn't just a pretence. Public opinion does matter, and demonstrators aren't shot on sight. Russia is quite similar to Iran in some respects, there is a genuine democratic system, it's just very limited.
If Russia's economy collapses, then Putin's whole narrative about how he restricted the peoples' freedom in exchange for stability and economic improvement might fall apart. Perhaps he can fall back on nationalism, and how it's OK to suffer for being powerful. Maybe that'll work, maybe it won't. Russians tend to be nationalist/patriotic (delete as you see fit), but does Putin want to take that risk for a bit of Ukraine with some outdated industry? Or the whole of Ukraine and a subject population of 30m odd, to buy off or crush militarily?
The oil technology and capital that Russia needs is mostly going to come from Europe and the US. While Russia can source other products from elsewhere, and get round sanctions, they'll struggle with those two. As has Iran. Remember that even the Russian oligarchs don't trust the Russian legal system, so they keep their cash in the West. Why would anyone else invest in Russia when its own leaders don't? Which is why so much of their borrowing is done in Westerm markets, mainly London, under more trustworthy legal systems. There are plenty of countries with money to lend, but they also like not to have it stolen, which is why they often do their investing via London or New York.