They aren't depleted. They've suffered 300K casualties, they have 24,700,000 left of fighting age. Also keep in mind Russia has no qualms about putting women in front line combat roles.
https://en.wikipedia.org/wiki/Casualties_of_the_Russo-Ukrain...
Also, Iran seems like they want to get involved. They've been selling Russia arms during the conflict. They have about 17 million people of fighting age.
https://en.wikipedia.org/wiki/List_of_global_manpower_fit_fo...
>do it in a weekend
They said that about the US Civil War
https://www.loc.gov/exhibits/civil-war-in-america/april-1861...
And WWI
https://www.theworldwar.org/exhibitions/over-christmas
By WWII, we realized it wouldn't be a short war. We seem to have forgotten. Also Russia has a lot of nukes, you know what MAD stands for right?
Best case we're probably looking at a Phyrric victory.
