Maybe I have missed something, but I do remember western intelligence agencies talking about how the war would cripple Putin's ability to control the oligarchs/crush the Russian economy and eventually force him from power etc.? Havent heard that line of thought in a while. In fact, I do remember reading that some of the oligarchs who spoke out against Putin have had some pretty harsh reprisals.
All this goes to say, no matter what armaments the west gives to Ukraine, if Putin remains in power, there always remains a chance of further escalation (more mass mobilizations, utlization of nuclear weapons, etc.). So by all means, lets give the Ukrainians planes and guns and missiles, this ends in a political settlement or a nuclear war. In my opinion, there is no path for Ukraine to simply expel the invading forces and end the war, it only ends when Putin decides he's had enough or he's won.