I thought that decision has already been made. The Sakhalin-2 project is one of the largest ever undertaken and had the involvement of the major Japanese players. It was to be the solution to the need for gas.
Even here, the article states that Sakhalin-2 project gas would be swapped for Kazakan gas payment to gazprom. There seems to be a lot there.
True, but technically Russia and Japan are still at war, and the northern territories are still the sticking point. It wouldn’t have been too difficult, I think, to present to the Russians the carrot of perpetual fuel sales and the stick of getting the territories back—it’s mostly fishing rights, certainly not like the issue of the Crimea, a place the oligarchs like to go to.