Saving face matters a lot for dictators, who often lose power if they embarrass their countries. For Putin this is now a matter of personal survival. He will do whatever it takes to avoid an outcome that makes him look weak to the Russian public -- he clearly doesn't care what the rest of the world thinks of him at this point.

You mean Alleppo. Idlib still under opposition/Turkish proxies.

From the Russian perspective:

If the country wont agree to NATO neutrality, the next best outcome is destroying it so thoroughly that it will be a humanitarian disaster for decades to come.

The former is a much more attractive option to them because it would pose the lest threat. The second is still favorable to a prosperous NATO and EU member.