Russia doesn’t have the population base and comparatively speaking, Russia is a much smaller country in terms of population than many other countries. For example, Bangladesh has more people at 142 million.
They might not run out of shells, but they could run out of recruits very soon. Then, holding the country is another matter even with a puppet government, an occupied Ukraine would be a hotbed for revolt.
The trouble is that we really don’t know what the truth is insofar as who is really winning. It’s been over a year and Russia hasn’t appeared to have achieved its goals which would probably be annexation of eastern Ukraine, a dictated peace treaty and installation of a puppet government.
I don’t think it’s really been worth it for Russia. They now face in a long term pariah status with losses in trade with the West. Whether they can make up these economic losses with China and non aligned nations is uncertain.
The capitulation of Ukraine.
Annexing territory isn't an accomplishment until the nation from which it is ripped accedes to it.
As long as Ukraine keeps fighting, Russia has not achieved any of its goals.
Regards,
Russia is far better positioned personnel wise than Ukraine is
70-90% of this war has been fought infantry wise by Wagner DPR and LPR etc militias
The Russian regular army infantry has had minor involvement
Partly due to being an arty war mostly