Good point, and the answer (at least to me) seems to be no. Russia is running out of soldiers and doesn't have the luxury of time to train more, thus it's hiring PMCs and trading tech with the DPRK in exchange for soldiers.
I honestly do not think Russia can sustain itself in Ukraine.
The Ukrainians are fighting to exist, so they'll find to the end. The Russians don't have this problem, which is why we're seeing so many people leave Russia since 2022 (it's also why Russia restricted emigration after 2022).
Something I know from my former job as a military intelligence officer is for you to study POW. I watch a lot of POW video from both side, and you can see the people in Ukraine conduct quite uniformally, they have similar equipment upon capture, that mean they are trained in the same way, being equipped to a standard.
Russian POW however, does not have the same standard over the year, I remember back when they were captured by the Ukrainian, their kit in 2022 is quite enough (still not the kit I would want to go fight a conventional war) but as we move by down the road, everything they carry has shrink One video I saw with a soldier being capture and stripped in 2024 and he is wearing minimal gear, rifle, vest (not even a body armour) and helmet, not enough food for 3 days (standard op pack) operation and just about enough ammo to last for a medium firefight (around 180 rounds, you need about 270-300) And their IFAK was missing quite a few things (Gauss, Scissor, Picks and no wet dressing) and it's so substandard I wouldn't have it at my home, because it did nothing, let alone going to war with that. No individual radio, optics, and no accessories such as VS Panel (Or whatever Russian equivalent to VS panel, which is just a folded flag but essential for not getting Green-on-Green by your own Airforce)
The reason this is the case is because Russian had expanded their military, yes, there are more people, but their equipment field rate are the same (or may even be lower, I don't know) which mean people are bringing in less gear to war to even things out, that never a good thing for an army, I would imagine Russian military probably is raiding those North Korean Kim send to Russia for Kursk, because suspiciously, they weren't wearing standard NK uniform, they were wearing Russian gear. It would make sense if they didn't tell you North Korean are coming, but they did, which make putting them in Russian gear no meaning at all.