>>"...As an option, yes, the most obvious one is that the end of the military operation will fix the demographics. ..."
The RU's demographics are beyond fixing. Their war on Ukraine has made things much worse (casualties plus major outflow of people fleeing mobilization plus a few people leaving on principle) but the RU demographics were dire *before* Putin decided to invade.
I think those dire demographics were one reason Putin decided to invade. Whatever the goals he had in mind (several geopolitical mavens think his goal was to re-occupy out to the geographic barriers surrounding the plain the RF is on*) he had to invade this decade - or he wouldn't have the military-age demographic to do it.
*note that those barriers are inside countries that are now part of NATO - so if those mavens are right, his goals were always *beyond* Ukraine.