Contracts can be amended. Russia has oil, gas, diesel, fertilizer products, nickel, palladium that the world needs. Not sure how this plays out except China making a ton of money.
Is the USA likewise required to pay in rubles?
And if Russia doesn’t sell their gas/oil they get $0. Sure Europe suffers but so does Russia they really don’t have other income sources.
But one thing is certain. Trump was 100% right.