having no internet means no fork, no different chain. it just means no competition from russia.
Cutting the internet connection doesn't take their computational resources. They can still use them to mine blocks, even if they had been using them to provide shares in a pool outside Russia.
there was no chain split when kazahkstan went dark last year. because no internet means NO INTERNET
I can think of many other reasons why they didn't split Bitcoin. One's that it makes consensus harder to be achieved. Another is that there wasn't enough demand for a fork to occur.