The Achilles Heel of general public use of Internet services has always been the functionality of DNS.
Unlike Layer 3 disruptions, dropping or disrupting support for the .ru TLD can be accomplished without disrupting the Russian population's ability to access information and services in the West.
The only countermeasure would be the distribution of Russian national DNS zones to a multiplicity of individual DNS resolvers within Russia. Russian operators are in fact implementing this countermeasure, but it is a slow and arduous process, and it will entail many of the operational difficulties that existed with distributing Host files, which DNS was implemented to overcome.
The .ru TLD could be globally disrupted by dropping the .ru zone from the 13 DNS root servers. This would be the most effective action, but would require an authoritative consensus. One level down in DNS delegation are the 5 authoritative servers. I will leave it to the imagination of others to envision what action that could be taken there...
The impact of any action would take time (days) to propagate.