A quick breakdown of what SWIFT is and why it matters
Think of SWIFT as a large Websphere MQ installation, distributed across several data-centers.
You get an IP access by installing a router, leasing telecoms connectivity.
You get access to publish/subscribe with an SSL certificate exchange.
You get access to send/receive to a specific node(Bank) with another SSL exchange.
It is important to realize nodes can only send messages to those addresses which have been trusted, i.e. keys exchanged.<p>So a bank (Bank-A) trusts you to send SWIFT messages, all you can do with these messages is make accounting debits & credits within that bank. e.g. please debit $100 from my account number 12345 to account 67890.
You can also chain the messages, something like, debit my account $100, credit the account of Bank-B, and send my message on to Bank-B.
The message to Bank-B might say (debit Bank-B and) credit John-Doe-account.<p>(It's the job of the treasury department within the bank to monitor & keep these nostro [other bank] accounts funded)<p>Perhaps not obvious, but banks don't have hundreds of correspondent accounts. So to send money from a small town bank in Peru, to another small town bank in Palau, there are going to be a lot of these back-to-back transactions. The pathways are determined by hardcoded rules - not by SWIFT - but by each bank in the chain.<p>So sanctioning SWIFT is one part. The other part is getting every bank on SWIFT to remove all correspondent banking rules going via Russia. (Quite nice work I suppose).<p>Since the messages themselves are just XML, and not partially large, you could easily put all the days messages which got rejected into a .zip & use email (I suspect this is common operationally anyway).<p>Any kind of sanction on SWIFT would instantly lead to private MQ (or whatever flavor of messaging) infrastructure springing up everywhere & total chaos for every bank in the world (i.e. quite different to Iran).
This would cause a reduction in the number of correspondent accounts each bank would be willing to maintain. So longer pathways, slower international payments.<p>I doubt SWIFT could recover from a sanction. It would just close down. The endgame being heterogeneous networks, poorer monitoring, so the USA lose.<p>The sanctions put on individual Russian banks can be monitored (by SWIFT). In likelihood they are not used as correspondent banks.<p>>How does the system guarantee that nobody's creating money without notifying everyone? 
SWIFT doesn't do this. I suppose a special audit is triggered (see Wirecard ) and the Auditor should catch it.