Ah, yup, SWIFTnet does indeed run over the public internet (apparently that changed way back in 2005, so my information is quite dated!) TIL!

The question then becomes: how is the network designed to handle DDoS attacks? For example, you'd need to identify the network segment or host IP address where the SWIFTnet connections are terminated, among many other things, and I have no idea how you'd do that and if the system builds in resiliency for things like DDoSes.

Of course, the simpler answer is just to blow up the ISPs and cut power to datacenters.

Regardless, if the Ukrainian banking system connection to SWIFT was indeed disrupted, you wouldn't be able to transfer funds to a crypto exchange in the first place, which rather undermines its use as a way to get funds out of the country...