Not much to think about. 

There are over 500+ undersea cables and more coming online every month. The Internet (and networks in general) are designed for resiliency and redundancy. Unless Russia could cut every last one, it's simply a fool's errand. Further, the cutting of cables would have significant economic impact to themselves as well as many of their allies. 

Lets just say if they embarked on this suicide mission, they would get rolled by the time they cut the first one. Again. Fool's Errand.

This sort of thing is floated by folks that simply don't have the technical knowledge to realize how beetleheaded it really is.