I'm sure that Russia will say, "Go ahead, sanction us." They will be staying put and the Crimean referendum to join the Russian Federation will proceed.
But circumstances have changed on the ground. Ukraine hasn't joined NATO and yet Russian boots are in Crimea. Nevertheless NATO should be sensitive to the reservations Ukrainians have about it. In this spirit, NATO could do is to pass a resolution inviting Ukraine to join. If, for some reason, there still existed significant domestic opposition, the resolution would leave the door open for Ukraine to either politely decline the invitation with thanks or it could reserve making a decision pending further consultation such as through a national referendum.
A NATO invitation to Ukraine would tell Russia that NATO would be prepared to defend Ukraine if Russia refused to withdraw from Crimea or made further advances. Now I understand that some members of NATO are more equal than others and this country would be expected to bear a considerable burden of that greater equality. It certainly doesn't help matters when the Obama Administration is cutting our military to the bone thus reducing its capacity to act in our national interests and on behalf of our allies.
Yet at this point Russia doesn't take the Obama Administration or the West seriously when it comes to Ukraine and that won't change with the imposition of sanctions. I realize that a NATO resolution which extends an invitation to Ukraine to join is not without its risks. But that's exactly my point. As long as Russia believes the U.S., the West and, by extension, NATO is unwilling to take a risk then Russia will pursue its national ambitions on the global stage undeterred. In addition to the subjugation of Ukraine it will also result in a weaker United States.