This is how I know you didn't read the article.

BK did cut the supply chain logistics. It's mentioned in the article.

Sue the franchisees? Where? In Russia? In the middle of an economic war with the west? Even if the suit proceeded for some reason, who do you expect the court to rule in favor of?

BK did everything to severe ties. The only thing that remains is to sell their share of the franchise. If they sell now (even if they find a buyer), they likely won't be paid in anything other than rubles which is useless.