First of all, not the entire world sanctioned Russia.
So while Russia has been largely cut off from Western markets, it may find less hostility to trade in various other parts of the world. While Russia’s oil industry is hit, and hit severely, it isn’t dead just yet. The biggest part of the story, however, is in the arms industry.
The Russian arms industry employs nearly five million people, and now accounts for 20% of all manufacturing jobs in Russia. A very significant portion of Russia’s GDP is funneled directly into the productions of missiles, bullets, tanks and other material needed to sustain Russia’s war effort. Growth of the overall economy is pretty much at zero as of last year, but it isn’t shrinking in absolute numbers, either, because Moscow continues to invest in its arms production. Other sectors, meanwhile, are dwindling; Russia is cannibalizing its own economy, sacrificing everything just to keep the war going.