1. Short war
Russia ramps up its military operations with devastating attacks. Thousands die, Kyiv falls, Ukraine's president is killed or flees, and Russia installs a pro-Moscow puppet regime. This would be an unstable outcome, vulnerable to insurgency and future conflict.
2. Long war
Perhaps more likely. Maybe Russian forces get bogged down, with low morale and poor logistics. They may struggle to control even captured cities. Over time, Ukraine's forces become an effective insurgency, while the West continues to supply weapons. Perhaps after many years, Russia eventually leaves.
3. European war
Putin could send troops into ex-Soviet republics like Moldova and Georgia, that are not part of Nato. Or there could just be miscalculation and escalation. Putin might take a risk if he felt it was the only way to save his leadership - if he faced defeat, he might be tempted to escalate further.
4. Diplomatic solution
By already agreeing to talks - even if they haven't made much progress - Putin seems to at least have accepted the possibility of a negotiated ceasefire. If the war goes badly for him, Putin may judge that continuing is a greater leadership threat than the humiliation of ending it.
5. Putin ousted
It might seem unthinkable. Yet the world has changed in recent days. If the war is disastrous for Russia, there may be the threat of popular revolution. And if those who have benefited from Putin no longer think he can defend their interests, such an outcome may not be implausible.
