To be honest, the best solution is that the take-over of Ukraine is swift and bloodless. We donot want a protracted war in Europe. I am not sure that Ukraine will have the ability to withstand this invasion and the speed of the Russian success is probably more worrying from a point of view that Putin will be emboldened if this goes well for his army. My gut feeling is that the take-over will be pretty short and sharp and that the Russians will have a more sympathetic leader in place as was the case with the previous president of Ukraine.
From a European pesepctive, I would guess that the Baltic states will now be concerned that they will be next. I am not sure that EU trade sanctions will have any impact whatsoever and may actually provoke further action by Putin as he seeks to recouperate the resources he will have lost as a consequence. I think that there will probably be a wave of cyber attacks by the Russians against European instiruation in response to the sanctions. There was a good aticle in the Sunday Telegraph the other weekend about the broader Russian influence in the Mediterranean which was described as almost as the forgotten frontline against Russia as few people are aware ot the extent they are involved in the politics of places like Cyprus. The Russians are chipping away, piece by piece, at southern Europe and it does make you feel that this is all rather inevitable. Any efforts to curtail the malign infliuence of Putin should have been done ages ago. The Russians feel that they can do whatever they want in Europe and I feel it is fast getting to the point that this is a reality.
I am not convinced that Putin will resort to nuclear weapons but this week has been salutory insofar that it is clear there is no appetite for military intervention by the West and that Putin probably has more freedom to do what he wishes that he ever believed was possible. This week has shown how ineffectual NATO actually is regardless of whether of not you agree with it's more assertive actions abroad from the 1990s onwards. I think Putin should have been isolated much sooner or greater efforts made to bring Russia in to the EU. I blame Putin for his aggression but the ever-assertive Russia is as much a creation of the west's inability to engage. Accepting the dodgy money from Russia has demonstrated how reliant the West actually is.