Negotiations might be tough and difficult but I would not speculate now decades or years
Russia has very few troops in the Ukraine. They are about to capture 5,000 Ukrainian soldiers including 500 foreigners. One brigade of 800 Ukrainian soldiers mutinied rather than return to the frontlines. The center of Ukrainian lines is close to collapse. Russia is mobilizing in July. That could be when they blow away what is left of the Ukrainian army and take Kharkhiv and Odessa. The war is almost over.