No they wouldn't.
Soviet military doctrine is based on attritional capacity "we have so many more troops than you we can afford to keep losing them - you'll run out before we do." Look at practically every Soviet military operation from Stalingrad onwards. Look at post-Soviet Russian operations in Afghanistan, Chechnya, take your pick.
Ukraine has a total population of 45m - at least it did before Putin started murdering them - and Russia has 25m men of military service-eligible age... Plus conscription.
Russia wants the gas and oil, and deployed troops it is perfectly happy to sacrifice in order to take control of the gas and oil. If Putin loses 100,000 troops to kill 100,000 Ukrainian soldiers, he'll have destroyed 50% of the UKR military for the cost of maybe 10% of his own. But his pool of potential conscripts is far larger and his crushing control of state media means he can draw drops from various parts of Russia and no-one inside the country would ever see the bigger picture.
He's not withdrawing in the face of 10,000 or 20,000 Russian casualties. Not a chance.