The reasons for the immediate action might be logical, but looking at the medium term consequences it breaks down completely in my mind. The only two possibilities I can see going forward is either a forever-war as in Afghanistan, or a forever-sanction situation like Iran or DPRK.

I don't see how any listed benefits would outweigh the costs of either option. It troubles me a lot, because Putin has seemed to me to be a carefully calculating player up until this. It makes me wonder if he has truly lost it. Or if there is some grand plan which this is only a small part of. Both are scary.