Those commanders will be prosecuted whether or not Russia "wins" the war. (I'm using scare quotes because there is no realistic scenario that could make this war a "win", so I guess what people mean by "win" as opposed to "loss" is in this case "permanently occupying Ukraine" at an insanely high cost.)
There's a big difference between them being prosecuted while living in a Russia (or Ukraine) that won't extradite them and instead rewards them for their part in a successful war, vs. them being prosecuted and Russia no longer being willing/able to protect them from punishment. Exactly where you draw a line of what you consider a win or a loss is subjective, as is whether that line is the same as the line for are these people are at risk of facing punishment from other nations (probably not, as if Russia announced a withdrawal of all troops tomorrow it would be hard to see that as a Russia "win", yet Putin would still have enough power to protect everyone by not allowing extraditions).
If they have committed war crimes, these commanders will prosecuted by the majority of countries in any case, no matter how the war develops and what happens to Ukraine. Of course, Russia won't extradite them. That's obvious to everyone. The idea (that you seem to peddle) is absolutely absurd that there is a scenario in which Russia would hand over their own military commanders to the International Court of Justice or any other third country justice system.
I agree I'm not expecting that to happen, but is it impossible a coup/revolution could happen that sees a new leader willing to agree to offer up some war criminals for any cases the ICJ brings as part of a post-war treaty to get sanctions removed? Surely crazier things have happened to countries' leaderships and smaller demands have been made in peace treaties.