Well; Let's say that in the first instance those who live on the border, where literally the cities are separated by a few meters, there is cellular connections available, of both countries, in this case one of them would be blocked.
I have been in border places where the Internet connection is better in Mbps that the neighboring and literal country sell these connections with the use of antennas that you can get on ebay and then an antenna point to point  of the other side of the border works.

The point is, I think way if they blocks access to the Internet it, it would not be a 100% blockade, somehow there would be a gap it would open an alternative communication technology, anyone who wanted to update a node could access it in some way. In fact, there could be a Lan network in a part of Russia that will become a WAN because of the fact of having someone nearby on the border.