No communist thinks that Russia is still communist. The critical support for Russia among some communists (me included) has to do with them fighting western imperial expansion/domination, and that Russia winning (or rather: not losing) would weaken the US empire and give breathing room to socialist and anti-colonial movements worldwide, since the US empire is the no. 1 threat to those movements. If US/EU supremacy on the international stage were broken, the US would have a much harder time isolating, toppling, or sanctioning socialist or anti-imperialist governments. If Russia loses and gets broken up or economically ruined, that would be proof of imperial power and scare other countries into caving to western demands. These countries would also lose Russia as a potential ally and trade partner.
The other major interpretation among Marxists (and there's been a lot of debate about this) is that both sides are imperialist, and the correct stance in this conflict is revolutionary defeatism (as Lenin preached in Czarist Russia, or Rosa Luxembourg did in Germany during WW1). In this logic everybody need to fight and overthrow their own bourgeois governments and stop the war (i.e. Russian workers should undermine the Russian government, while Americans need to fight the US government), since the working classes of those countries shouldn't fight each other, but rather fight the capitalists in their own countries. Slogan: No war but class war.
There was plenty of evidence that this was the likely outcome of this offensive months before it even started. Why tf did they go ahead with it anyway?
I remember discussing the Russian advantage on reddit back in January, including them building defensive lines and the general imbalance in equipment, especially artillery and ammo, as well as the fact that Russia had caught up in troop numbers by that point. I had western sources for these numbers.
You wouldn't believe the level of hate and name-calling I received for pointing this out and saying they should negotiate. But apparently I was the one spewing propaganda.