The problem with sending peacekeepers in is the effect of drawing a line where the UA and Russian troops are engaged. That line over time unwittingly then becomes a de facto border that Russia can claim has vindicated their original political aspirations, except it will likely be more West than the Donbas and closer to the Dnipro. Do we think Ukraine would accept that? Not at all.
I still speculate the long game is Russia loses militarily, politically with social unrest and a change of regime. The more damage is done to Ukrainian people and property the more likely this is to happen, eventually. The West can then engage with Russia, metaphorically beat them up a bit, turn the psyche towards European integration but on a democratic mandate. There is then only one bad guy, in Asia, allowing a sharp focus to constrain their ambitions with the benefit of substantial natural resources having been collected on route.
This is a 30-40 year plan. In the meantime no western army is engaged in Ukraine, in large numbers, other than a testing bed for the evolution of higher tech weapons including drones in particular. Wars can bring advantages to protagonists whether it’s securing natural resources, political change, training, disaster capitalism, showcasing weapons, each to different degrees.
Bear in mind this war could be 7 years into its 40 year plan.