If they keep at it, they will win; the military balance is too much in their favour.
Having conquered, they will then block out all content which carries truth and replace it with propaganda, just as it is in Russia.
You argue we must keep the Internet open and accessable to Russia, both in this situation, and for it to be used in this way.
Without physical intervention.
I don't think this is true. The root DNS servers ICANN runs could stop handling requests for anything on the .ru/.su Russian TLDs. Though Russia runs the .ru servers internally, from ripn.net, there's still reliance on the root servers to point there. This would break Russian internal access to their own services.
If you run `dig +trace government.ru` you can see your first query is to the various "*.root-servers.net" name servers. When I did this my queries went like this:
A.ROOT-SERVERS.NET -> B.DNS.RIPN.NET -> NS2.GOV.RU
Now, to be fair, significant, though temporary, damage could be done to them from the outside (who knows how many Russian systems have their DNS configured to 1.1.1.1 or 8.8.8.8, for example).