If you think that the global banks do not use messaging services for cross-border transactions then you are wrong. It is known as Society for Worldwide Interbank Financial Telecommunications (SWIFT) and it is going to solve for the majority of banks for cross-border payments.
Imagine how would you feel if the "group administrator" blocks you out from the group chat that you were dependent on for your daily work. This is what America aka unofficial group administrator of SWIFT is proposing for Russian Banks in case there is an invasion of Ukraine.
As per previous trends, such bans have applied even with some resistance from other countries, In a recent case when sanctions were applied on Iran banks some European banks did put in a protest but for not long as the USA threaten to pull out from SWIFT.
A ban on Russia would not have a similar impact but will have a much larger impact. Even though Russia has been anticipating such a ban since 2014 and working on its systems and payment modes as a back the impact to many European countries and companies will be much larger. For example, thirty-five percent of the natural gas requirement of Europe is fulfilled by Russia and it is the fifth-largest trade partner for the bloc.
Such a decision would also alert other countries of any future risk on full dependency on SWIFT and lead to a reduction in usage over time with some parallel solution. One such example is the BRICS bank that supports Brazil, Russia , India, China, and South Africa without the usage of SWIFT
In the end, it has become a true Russian roulette as any overconfidence in pulling the trigger will result in irreversible consequences almost equal to a bullet passing through the brain.