Germans were playing a fair game when it comes to the pact with Russia and followed the procedures. Fair as fair a partnership between crooks can be when spoils are waiting to be split. The Germans were tied in the campaign in the west and could not afford to set it on thin ice in the east. Russians on the other hand where doing much to take advantage of the moment. When it comes to Poland, it is unclear when Rusians were to move in to take their spoils. For Hitler it would have been more convenient if the Soviets attacked Poland at the same time or soon after, one or two days later. That would put Soviets on the same level as an aggressor state and partially freed Germans from the guilt. Either that or not move in at all. Then they took Bessarabia when Hitlers army was tied in the west. Bessarabia is next to romanian oil fields which for Germans were crucial. It was possibly an act to show Germans that the Red Army could at any moment move in to take the factories and cut german oil.It was enouh to make Hitler start pounding his head against the wall.The baltic countries and parts of Finland were occupied to shore up Leningrad with more land. Hitler agreed only because he had no choice facing coming war with Poland. The demand caught him naked. He said they would take these lands anyway sooner or later. But now he had to walk his army some 700 or 800 miles to reach Leningrad allowing Sovites plenty time to shore up the city. Inntially the baltic lands were to be left alone. That in turn was not acceptable for Soviets, because Germans could at any moment find an excuse for some german miorities having been beaten or someting like that and the need to help them. They could move in a matter of a few days as they did in most of Europe. Leningrad would be then in sight,just next door, waiting for an immediate assult. The Soviets wouldnt have it. They did everythig to use the M-R pact to strenghten their position against Geman upcoming attack,but in a way that was unclear and burdensome for Hitler. Pact was just a pact A piece of paper, no without the small print. The problems that followed when it was executed made the stelmate unbearable for Hitler. He had gotten what he wanted keeping the east calm for a while, but the Soviets made him pay for that.I am not saying he wouldnt attack Russia if the Soviets played a nice game keeping their hands off Europe altogether, but all these moves in the eastern part of Europe on the part of Russians made him snap in 1941 and not later. The soviets left him no choice. They themselves did what was right to shore up the western borders, mainly the Leningrad area with more land. They had no choice themselves. Sometimes the guilt kind of comes from nowhere. That's why I am buffled Stalin and Molotov were so easily fooled and played into german hands when push came to shove.
Anyway, it has not much to do with Stalingrad and the effects of possible German Win at Stalingrad. The north front was part of Barbarossa meaning part of Blitzkrieg, but it had little merit in terms of land resources. Bypassing it meant possible attack on Germany from the area of the Baltic sea. Germany had already been showered many times by allied bombers, so what the heck. It required strong defence lines, just like the center required strong defence lines. The south was much more of a prize. Ukraine had already been taken. Had oil factories fell into german hands ,the Nazis would have been fixed for good. They didn't need Moscow or Leningrad. As later events showed they didn't give a damn about their own population. All they needed were strong defence lines in the north and center and resources in the south. Slave labor was in abundance for expolitation, either by shiping it to Germany or in place. It would require building quickly an infrastructure to make it going. Time was essential, but now they would have all raw resources needed,perhaps some of the machinery could be saved.They would have labour and food, mostly oil, which was prizeless.Nothing needed to be transported and overstretched.It comes down to capabilties of german armies to keep Russians at bay and settin up pretty fast industry in the south. It was all Hitler had left when he moved the offensive south, but it was still plenty. It was easier to think of crashing the enemy althogether in 1941 without the burden of expierience of what followed, but the enemy wouldnt disapear. Even with the success of Moscow and Leningrad. It would simply move east and south to regroup. Much of the south with oil would still be in Russian hands. In the long term the south with all its resources would pay more than Moscow and Leningrad together. The operation Blau despite having been introduced as an alternative after setback in Moscow and Leningrad could have been the primary objective, replacing Barbarossa. Besides an alternative timeline and alternate chain of events, it was hardly posssible. I don't think that any german top head was cosidering it in 1941. In 1942 it was born out of the blue, yet it was a good one, and much more realistic than Barbarossa.