You think a former Super Power with thousands of Nukes will accept defeat..? I can see a scenario where Putin will use tactical nukes on Ukraine forces, how will Nato react ? Use nukes as well and risking a full escalation of war on European Union countries ? Highly unlikely, but Putin using nukes is a very real possibility.

The USA & Nato gave Ukraine support and chance to defeat Russia, but the support is not without conditions, USA is going into election next year, the Republican is not 100% supportive of Ukraine. Time is on Putin's side. The Europeans are running out of patient with the war at their door step. USA & Nato will force Ukraine to accept cease fire and creation of a Buffer zone a DMZ between Nato & Russia. Ukraine will end up like North & South Korea. What choice does Ukraine have ? They are 100% dependent on Nato help, they must listen to Nato's instructions.

How NATO will react ? Using nukes ? More Sanctions ? No, NATO will highly likely to tell Ukraine to accept a seize fire and surrender territory to Russia.

The West will not confront Russian in an armed conflict directly, so Ukrainians are proxy for the west. deplete what ever military the russian armed forces may have ..obviously history did not teach us enough. Russia has more Nukes than the west, they have means to deliver them to their targets. Any attack on Russia by the west will be responded by Nuke strikes, tactical or inter continental..