It's not a matter of "again". Gas purchases are not on the table as far as sanctions go. It's the other way around. The EU is afraid that if they impose serious sanctions Russia will cut off the gas supply. This will hurt the EU far more than it hurts Russia in the short term.
It is certainly a last resort option, but on the face of existential threat, denying Russia a major source of income to finance the war is a legitimate goal.
The major point of Nord Stream 2 was to remove this PoF.
That's the wrong perspective. You have to remember that even at the height of the cold war, the Soviet Union was still providing gas to Europe. This has always been the arrangement. Ukraine stopping gas is not denying Russia income. It's denying Europe a critical resource.
