Have to be a bit careful with my wording, because I do want to make clear that I don’t mean this as a “what if” scenario, really. I’m not asking how it would have changed the course of the war, more asking how their experiences compared to that of similarly large cities that had fallen during Barbarossa and after.
To say that Leningrad suffered from its siege by Finnish forces and the Axis powers would be an understatement. I probably don’t need to go into why - the death toll, destruction, and famine are fairly well known.
What I am curious about is both what the Nazi plans would have been for Leningrad if they had successfully taken it - as they did other major Soviet cities such as Kiev, and other Eastern European cities such as Warsaw (though Warsaw is, as everything is I guess, a special case) - and how much the soviets would have been willing to pay in all senses to retake it. Did holding on, ultimately, benefit the citizens there in any way, shape, or form?
Is there any merit in the idea that though they would have suffered terribly either way, Leningrad would have likely seen less horror if it had fallen quickly? Or is it really impossible to say?
It's clear that they would have suffered badly either way. Long sieges are notoriously bad for the health of the civilians involved, and usually a quick surrender is better for the health and safety of the civilians except in cases of major killing during a sack of the city following surrender or a massacre of the population. That the answer is not so clear for the case of WWII illustrates the brutality of the German occupation.
Estimates of the civilian deaths during the Siege of Leningrad vary; the more reliable estimates tend to be about 1.2 million, about 1/3 the pre-war population. Estimates are complicated by an unknown number of refugees, possibly as many as 500,000, moving to Leningrad before the siege. For comparison of an occupied city, we can consider Kiev, with a pre-war population of 900,000 to 1,000,000 (so about 1/4 the size of Leningrad). Again, estimates of civilian deaths vary, with an estimated 200,000 residents murdered during the occupation, and another 100,000 sent to Germany for forced labour (many of whom died). What is reliably known is that the post-war population was about 1/3 of the pre-war population. What is unknown is what fraction of that missing 2/3 of the pre-war residents died, and what fraction were alive but didn't return to Kiev. Smolensk suffered badly, too, with a post-war population of about 20% of the pre-war population (30,000 of about 155,000), and in the Smolensk area, about 150,000 civilians were murdered, and 160,000 sent to Germany.
That the civilian deaths in Leningrad were not higher is due to about 1.5 million residents being rescued during the prolonged evacuation operation (supplies in, people out). The death rate would have been even higher without the partial evacuation (since there would have been more people and only the same amount of food coming in). However, the genocidal treatment of the people in the German-occupied territories, and German willingness to starve the people in order to send more food to Germany means that an occupied Leningrad might well have suffered worse than occupied Kiev and Smolensk. "Genocidal" is not an exaggeration - German intent was to substantially depopulate the occupied territory to free it for German settlement, and to destroy the cities in order to eliminate Russian culture and communism. For example, about 30% of the population of Belarus died.
Given the choice of starvation during the siege, and probable starvation if they surrendered, along with systematic murder and deportation for forced labour, neither resisting nor surrendering were attractive choices. At least resistance allowed a significant part of the population to escape.