Frozen vs Confiscated…
Assets are frozen so they can’t be used to further the aims of the war, or in the case of Iran, to further the need to compel more acceptable international relations (i.e. nuclear ambitions). In a way, it’s based on the legal principle known as the “500 pound gorilla”.
Of course, to confiscate assets in the west, where the rule of law presumably actually works, the assets need to be shown as part of some wrongdoing. The current pretext as I understand with oligarchs’ assets is that they are active participants aiding and abetting the pursuit of the war and other criminal enterprises. The current oilgarchy is (allegedly) closely tied to Putin and their wealth contributes to the support of the entire Russian misgovernment, and they hold wealth only through the acquiescence of Putin and his government. (see Mikhail Khodorkovsky - Wikipedia for consequences of disagreement)
My thought is that Putin will eventually have to concede and withdraw, with various levels of concessions. Otherwise, the level of military and sanction support of Ukraine will continue to escalate until Putin has used up the 60-year-old veterans and has to turn to 70-year-olds and 14-year-olds to man the army, something usually done for defense, not offense.
One of those concessions will be repaying the cost of rebuilding. There are bridges, roads, rail, power grid, water and sewer to be rebuilt. There will be problems with food supply if much of the wheat fields of Ukraine cannot be planted in the next two months. And the most obvious from the news reports, there are probably millions of houses and apartments to be rebuilt, huge swaths of the population will be homeless for the next few years.
If the cost of rebuilding is not part of the peace treaty, then I would expect the west to use the frozen assets to go toward the cost of rebuilding. I expect that will not be enough, and I expect that a substantial portion of oil and gas revenue going forward will also be tapped to go to Ukraine. Basically, at this point Putin is mortgaging Russia’s future. You think the Russian economy was sluggish before, imagine it with more than half the oil revenue missing. the economy of a victorious Ukraine will be booming, with plenty of jobs in construction financed by this outside revenue.
Also, the cost of rebuilding will not be paid by the west if Putin actually wins, and occupies Ukraine like he wants to. Nobody in the west is going to send money to line the pockets of connected Russian contractors pretending to rebuild destroyed apartments.