soldiers are faced with the choice of being prosecuted for their crimes or fighting until the end

Soldiers don’t make the decision to keep fighting in this context. If Putin decides to retreat, the soldiers don’t go “whelp, if we keep fishing we can’t be prosecuted for war crimes” and ignore orders.

Large scale warfare isn’t the same as a single battle where there is a fear that surrender is worse than fighting to the death.

The incentive is Russia not continuing to lose staggering amounts of troops invading a country they share a border with. Russia could argue civilian casualties via fog of war and other typical war crimes excuse. You don’t accidentally rape in war. The only reason you try to get amnesty for it is if it’s SoP and it’s a tool you’re preserving for future conflicts. Things like rape, kidnapping children and even gunning down clearly unarmed elderly civilians in close range should be outside of scope and not applicable for amnesty by law. I’d also put it to you that even the most morally devoid, ghoul of a human would prefer a jail cell as opposed to dying slowly from being half disintegrated by a drone. Even for the hypothetical few that wouldn’t; the rest of the combat force shouldn’t have to pay that price.

In October this year, the Ukrainian Defence Ministry has released an intercepted audio recording of Colombian mercenaries serving in the Russian forces.

In the intercepted exchange, one of the field commanders gives an order in Spanish. Quote as translated by Defence Intelligence of Ukraine:

“When fog or mist conceals their identities, they must eliminate all people who are enemies: on motorbikes, on bicycles, women and children, women and children.” – Source

[Edit typo.]

If it’s always been like this then oh well 🤷🏻

There is no incentive to lay down arms for these people if they don’t have the option of amnesty.

You are assuming they are fighting directly out of their own free will. That was never the case; they were always sent there by the regime, and by now most of them have been forced anyhow. Seriously, if what the Russian-side soldiers want played into it, the war would already be over.

it’s been a part of peace deals since the dawn of time

Here is a - supposedly incomplete - list of convicted war criminals.