SWIFT is not the only way to exchange money. The actual power doesn't suffer from it being cut off. I do. And also from problems with card payments in the interwebs where MC or Visa is expected.

Also I don't think you realize how much money the Russian gang had in the open and hidden, one can basically say their credit is infinite. Other than trading national resources, they can, unlike American governments, cut local businesses and entities like lifestock to get more. They can do drugs trade, with their size it doesn't bear any consequences at all, Russian (and Azeri, and Israeli, and which not) embassies have been caught with smuggling industrial amounts of heroine all over the world, nothing followed after those cases. They can just catch people on the streets and sell them for organs and they do. They can extort. They can confiscate. They can enslave.

They are inefficient, for gangsters they are cowards, for mafia they are dishonorable, for cutthroats they are weak, for fanatics they are dirty, for thieves they are tainted. Nobody respects them. But that doesn't matter when you have such a shitload of resources.

They've spent hundreds of thousands of people in the last few years just for fun, to come to the same idea of war that has been found in Syria and in Latin America and in African conflicts without such a process. No way they are this stupid, but they wanted to feel this kind of power because there are not many things for them to want anymore. And also to kill brave people.