Vladimir Putin is in plenty of trouble on his own turf, and if not out of power within the year, will certainly be presiding over a much diminished nation. The Ukrainians have more than demonstrated they can carve big holes in the “blitzkrieg” army sent in by Putin, and its command structure has been put under great stress.
Keep the Ukrainians well supplied with the necessary tools of war, including trucks so they can maintain their own logistics, just keep actual footprint OUT of the Ukraine.
I would be very cautious about making any predictions about the course of this war. I would suggest both sides take a look at the outlines of the Boer War (actually at least two wars). The British Empire entered for what they thought were good reasons (including the mistreatment of black Africans by the Boers). The German Empire provided substantial aid to the Boers. The end result was the Boers still lost, the tactics and strategies the British employed to win the war hurt their reputation, and the German aid contributed to the souring of relations between Germany and Great Britain.