However, official casualty figures usually mention the number of “missing”, as well, which also includes those captured or deserted.

If the 2 Mar figure is to be believed the 9861 number seems a little high for mid-March, but in the chaos of combat, even the best efforts to keep track of casualties sometimes are inaccurate.

But keep in mind, if the total Russian order of battle is between 1-2k men, then only a small percentage of that is actually front-line troops exposed to enemy fire.
So even losses of several thousand are really devastating. This may be one reason why Putin has resorted to his scorched earth tactics. He simply can’t fully reinforce his front-line formations any faster, these are mechanized troops, not just plain grunts, and he is conserving what he has left. He needs to replace his combat and supply vehicles before he recommits these guys to the fight.

This is turning into a classic war of attrition, except that the two sides are running out of different resources. The Ukrainians are doing very well on the battlefield, both in terms of personnel and materiel, but their civilian losses and the destruction of their cities must eventually degrade their morale and combat effectiveness. Young men may be motivated to fight to the death for their country, but watching their families and friends slaughtered is something else.