The Boomerang Effect of Sanctions
There is a problem that will inevitably arise in the use of sanctions against Ukraine, which I am sure everyone reading this has already thought of. The problem is this, What happens to the sanctions if Ukraine becomes part of Russia or a mere proxy state? There will be a point at which we will have to sanction Ukraine; otherwise, Ukraine would be used to circumvent the sanctions—Russia will simply have goods and services brought in through Ukraine.
If we drop the sanctions in order not to punish the Ukrainians for being invaded, Putin now has an incentive to end the war more quickly and perhaps more brutally. If we don't, then we have to be comfortable with hurting the very people we wanted to help.
I think you must, if Ukraine falls and becomes a proxy state or a part of Russia, extend the sanctions to include Ukraine itself. Punishing Russia is, at the end of the day, more vital than helping the Ukrainians. In part because we are not only seeking to deter Russia from further aggression but because we are seeking to deter other nations like China. These are the sad truths of geopolitics.