The longer it goes on, the more bitterness, anger and resentment will grow among the Ukrainian population. This, along with stories of bravery and strong leadership, will only fuel the resistance to, and the and rejection of, Russian control. It will make Russia controlling Ukraine near impossible. Whilst it is easy for a superpower to flatten a country, controlling it is a different matter.
No-one will 'win' this conflict. Not even Russia, regardless of the weapons they use. If anything is futile, it's Russia's efforts. In the long-term, Ukraine will be an independent country and Russia will be a pariah state.