I wonder if the 50 % can be easily replaced or not. Some thoughts:
The first thought is that come one on, they can just bring in benzine and diesel from other parts of the Russia, and that's it. Yeah, 50 % of local production capacity was lost, but there's still plenty available elsewhere. But. But, at the crude oil has been coming to the refinery by pipes. Benzine and diesel don't come by pipes. While the Russia does actually have diesel pipelines, their capacity is already in use and they are not of help. So, the same amount of liquid that used to come in pipes now has to be transported from faraway refineries to Moscow by trains. I don't think that's a small feat at all, especially with Russian Railways' current troubles with wagon maintenance. They will probably be able to pull it off, but it will be damn expensive, it will overload the railway network even more in a time when there's no money available for repairing the wear, and it will cause congestion that hampers the Russia's military transportation ability.
Half of Moscow's fuel is a lot indeed. This will make the fuel noticeably more expensive in Moscow, and that means that everything that needs a truck to transport it will get more expensive as well.