40k sounds a little low if they're including conscripts and criminals.
It's hard to overstate how crucial the last Russian intervention was. The actual East Ukraine rebels are not that numerous or competent, so the Ukrainian regulars had them dead to rights, pinned down in Donetsk and Luhansk. But they naively thought that Putin might actually respect the border. When the Red Army rolled across, they caught the Ukrainian forces in the flank. The Ukrainians were first forced to retreat from south of Donetsk, and got badly mauled in the process as they had to pass through a choke point that the Russians pounded with Grad missiles. Then they got pinned down in Debaltseve and finally fled after a couple of weeks' worth of siege warfare. Debaltseve is an incredibly critical junction, lying squarely between Donetsk and Luhansk.
So with these two actions, from a strategic standpoint, the Red Army not only managed to inflict heavy losses on the Kievans, but also were able to link up their two primary centers of gravity, shore up their flanks, threaten Mariupol, and cover it all with a favorably-timed (for Russia) ceasefire. Any counterattack from Kiev now would be into the teeth of 40,000 reasonably dug-in Red Army troops, and conscripts or not, that's a tall order.