But it also offers an interesting test case for the proposition that investment banking businesses are now more fragile, as a direct result of the rules to keep the institutions which house them safer.
Rarely do business lines switch off quite so abruptly, giving bank management a stark choice of whether to stay or to go.
Bonus rules are supposed to keep bankers from doing risky business — but push up salaries, raising the cost base of any product line. Local capital and liquidity rules can make marginal geographies prohibitive.
Together, these changes push up fixed costs right across investment banks, and that should make the decision to cut and run easier. Rather than keeping teams together on basic pay, slashing lending and waiting for the market to turn, high and sticky fixed costs mean exiting businesses entirely early on.
But high fixed costs driven by regulatory change are just an excuse.
Investment banks have never, in modern times, found it easy to find the middle ground between stomping on the brake or the accelerator.
The collapse of the securitization market in 2007 and 2008 pre-dated the present raft of regulatory change, and banks had no compunction about slashing teams. More sensible institutions tried to reassign rather than cut, but banks which did — Morgan Stanley, for example — have not been punished. Deploying balance sheet has proved more important than having the same bankers covering the same clients.
When sanctions are lifted, Russian volumes will bounce back hard and fast. Banks that have left the business will be left behind — but will be able to catch up if they want it enough.