If Putin did that how long before he is assassinated?
Russia would be utterly and completely humiliated and become subservient to Europe.
China's economy is already in the process of collapsing, if Russia capitulates in Ukraine you will see the BRICS alliance begin to collapse. France and Saudi Arabia would immediately bounce back to the US dollar and then BRICS would collapse.
Russia has allied itself with Islamic nations, and with China. This alliance is not about Ukraine, it is focused on dethroning the US and Israel. He is using Ukraine to bait the west, to clear out their prisons, to get rid of old equipment, and Putin is all about restoring the USSR to a position of prominence. He would choose to die before he would capitulate.