It is generally a terrible mistake to assume that people are even remotely capable of reason. Thus, rational arguments against something are rarely convincing. Putin, isolated and riddled with delusions of grandeur, surrounded by sycophants and devoid of real-world information about his catastrophic invasion, is one of the least rational people imaginable. Moreover, given his cynical worldview, it's easy to see he cares nothing about the Russian people. To him, as to Stalin, they are merely numbers on a sheet of paper and as such, entirely disposable. No doubt, were he less ignorant, Putin would quote Louis XV and declare после меня, потоп.

In fact, Putin seems perfectly happy to use the old Stalinist approach of sending out wave after wave of cannon fodder to soak up Ukraine's munitions in the hope that they will run out of bullets before Russia runs out of warm bodies. As he's conscripting men up to the age of 50, most of whom are in shockingly poor health, there's no other logical conclusion to reach: they are simply there to die for his inane dream of a New Russian Empire.

For Putin's successors, if Russia doesn't just fragment into sub-states, each ruled by a thuggish overlord, most Russians who've recently fled will return once things settle down. So the drain of youth & talent caused by hundreds of thousands of Russian men fleeing the country is potentially only a temporary phenomenon and we shouldn't over-state its importance in either the short term or the longer term.