Putin can save face and leave the Ukrainian theater securing concessions such as Ukraine not seeking or accepting membership into NATO. Like all dictators, he can then see himself as a historical hero
One of the biggest fears the West has is that actions on their part may trigger the possibility of Putin launching World War III. If military aircraft is given to Ukraine, the story goes that Putin will turn to nuclear weapons in retaliation.
The flaws in this way of thinking are many and tragic if allowed to persist. First, Putin has clearly shown that any signs of weakness are dealt with by additional forceful and aggressive actions. The Russian leader is a bully and avoids confrontation with those willing to push back.
Putin invaded Ukraine under the feeble leadership of President Obama and Biden but bypassed any such activities while President Trump was in office. This avoidance indicates that Putin is far from a "crazy" lunatic looking to end humanity with nukes and is instead a strategist seeking the quickest and least costly way to accomplish his goals.