With no PoDs prior to March 1917, how can the
Socialist Revolutionary Party, the Mensheviks, some other (leftish) socialist party, or some combination thereof, be the ones to govern (or "govern") Russia in the years following the Revolution, instead of the Bolsheviks? At first glance, this should be doable -- FWIG the SRs held majorities in the Soviets, and won the parliamentary elections in November 1917, the Mensheviks were more influential than the Bolsheviks, and even Kerensky was a Trudovik (a breakaway party from the SR).
So, maybe Lenin is killed at Finland Station or isn't transported east? Or something else? However his faction's takeover is prevented, how does this alternate Russian Revolution run its course? How is the Russian war effort affected (or is that one of the conditions for stopping Lenin's Bolshevik faction)? Is it possible for the Revolution's leaders to at reject -- at least at first and in theory -- the "vanguardism" and/or "democratic centralism" of Leninism? Or can that only guarantee the failure of the Revolution (falling to right wing militarists, etc)? (I'm also somewhat drawn to the ideas of Nardonik remaining influential longer.)
(Note: I ask this as someone less than perfectly versed in leftist ideology and Russian political history; so, from those who are, forgiveness if I make mistakes here or struggle with some concepts.)
The OP raises some legitimate questions, which in my mind are worth exploring.
The Mensheviks and Right SRs
did have majorities in the Petrograd and Moscow Soviets, but the Bolsheviks prior to the October Insurrection would sweep up both.
There's a book by the revisionist historian Alexander Rabinowitch on the July Uprising that lays out why it was the Bolsheviks and not the moderate socialists who'd taken power in 1917.
The book in question is
Prelude to Revolution. Basically, a mass of workers, soldiers, and sailors poured into the streets demanding the implementation of Soviet power. As the Mensheviks and Right SRs at that moment had more or less controlled the Petrograd Soviet, it was assumed by the people in the streets that those two particular parties would have to seize power away from the Provisional Government.
They didn't. The July Uprising petered out, as most spontaneous demonstrations tend to do throughout modern history, and the Bolsheviks were blamed by the moderate socialists for supposedly having caused the unrest.
Even the admittedly anti-communist historian Orlando Figes admits in
A People's Tragedy that the July Uprising was
not a Bolshevik coup or even a Bolshevik-led event. Instead, it was a popular grassroots movement sprinkled here and there with Bolshevik activists that genuinely hoped that the moderate socialist leadership in charge of the Petrograd Soviet would embrace Soviet rule at the expense of the Provisional Government regime.
In Figes other book entitled
Peasant Russia, Civil War, it is made clear that by postponing the question of revolutionary land reform until after the Constituent Assembly met and made its decision on division of the land the Right SRs specifically were left in the dust of mass throngs of peasants seizing land violently from landlords long before the October Insurrection and even longer before the Constituent Assembly's first and only session in 1918.
If the Mensheviks bankrupted themselves in the eyes of workers, soldiers, and sailors (who would after the July Days protests gravitate more and more towards the Bolshevik Party), then the Right SRs did so in the eyes of the peasantry, their traditional constituency.
Furthermore, the Right SRs and Mensheviks, despite having bankrupted themselves, only wound up in control of the CA and therefore in "control" of Russia only happened because the splinter Left SR Party's chosen candidates weren't placed on their own separate list. Rather, they were bunched together with the Right SR candidates on the same list that was designated as the Right SR list.
As such, although most of the peasantry had gone over to the side of the radical socialist Left SRs, they nonetheless voted in record numbers for the Right SRs in utter confusion upon examining the bungled party election list.
The CA would be dissolved with the vast majority of Russians-workers, peasants, soldiers, and sailors-not caring at all and instead throwing all of their effort behind supporting Soviet power all the more so now that the moderate socialists had been decisively (and fairly embarrassingly) defeated.
Soviet Power
was Bolshevik power to a large extent, not to discount the role of the SRs in realizing and hammering out Soviet power that is.
By the time of Brest Litovsk, there was already a fairly stable if somewhat divisive two party Bolshevik-Left SR coalition government in place. The multiparty regime had forced the Menshevik and Right SRs out of the soviets a while after the CA's shutdown with hardly anyone protesting such a controversial decision (the same can be said of the banning of the reactionay Kadet Party, whose support merely melted away after its banning and successful suppression)
Thus, there already was a Soviet government in Russia - making the "government" that the Menshevik and Right SR claimed to have the sole authority to form after having won the CA elections through a legal loophole was a farce.
I would also strongly caution against adopting the "Great Man" theory concerning Lenin. He himself failed to predict that on the 25th of October the armed wing of the Petrograd Soviet, the Military Revolutionary Committee, had managed to galvanize the support of a large but vocal minority of workers and army garrison soldiers in overthrowing the corrupt, conservative, and hopelessly reformist Provisional Government under Kerensky.
Lenin may have got the Bolshevik Central Committee to approve of an uprising on October 10th, but needless to say the planned uprising simply fell by the way side and would never come - meaning that if the CC decision was supposed to be a coup masterminded by Lenin then it was a very, very, VERY, poor one at that.
Red October, the actual insurrection, was carried out entirely from below after press workers told the Petrograd Soviet, the MRC, and Left SRs and Bolsheviks (with Lenin nowhere to be seen, never having been present until midway through the insurrection when he effectively told the MRC to do what it was already doing: that is, going on the offensive against the regime and bringing it down as soon as possible as to better protect the Second Soviet Congress)
The most realistic way for the moderate socialists to take over is through a military coup occurring in 1918 in Petrograd - a very real threat to Soviet power that very nearly succeeded had not a few mistakes by the conspirators tipped the Cheka off about the planned overthrow (somewhat ironically) of the Soviet government, when, like the Provisional Government was vulnerable to attack by an armed force.
The Cheka, as the immediate and necessary successor to the MRC, just barely staved off a successful counterrevolution in the capital.
Had it not done so, had it not been tipped off prematurely, then the moderate socialists along with the banned Kadet Party could potentially do away with the Bolshevik-led Soviet government, dissolve the popularly elected soviets, and reconvene the CA.
Buts that's assuming that the moderate socialists have enough strength to assert themselves into the inevitable political vacuum created by the destruction of Soviet power.
More likely is the rise to power of a conservative, right wing military regime keeping the capital under martial law and moving to pacify Red Moscow assuming that those loyal to Soviet power have enough resolve as to make a last stand and hold out against the impending attack on the city (or domestic unrest, spearheaded by right wing conspiratorial groups that had lost Moscow to the Reds, that take their chance in the ensuing confusion to rip the Moscow Soviet a new one)