Apocalyptic Mess
"Now, Lucifer is free. The Apocalypse is here. Angels with hidden agendas are applying pressure on Dean to take his special place in a spectacular battle to slay Lucifer and bring Paradise in a battle sure to kill millions. Dean refuses to help at the expense of so many human lives. And so, against a landscape of escalating celestial violence, natural disasters foretold in the Book of Revelation, and a rising human death toll, Sam and Dean scramble for a way to do the impossible: Kill the Devil. Their only ally: Castiel, now Fallen and a fugitive from the armies of Heaven."
"The fifth season [of Supernatural] revolves around the fight to stop Lucifer and save the world from the Apocalypse."
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Dean is conflicted about whether he should give his body to Micheal (because he's Micheal's vessel) or stop Lucifer with Sam. This makes for a good plot and whatnot but a heavy concern of "the gang" (Bobby, Dean and Sam) is the lives of "innocent" people. Pa-lez give me a break. Regardless of what they (mainly Dean) choose, choose Micheal or kill the Devil, millions of people are going to die anyway.
What is it that makes them think that more souls will be "saved" if they postpone the Apocalypse opposed to if they don't? My opinion is that more souls will be lost if they don't accept the fact that "the world is ending."
Also on the souls subject, by "saving" if they mean more people will live and not die, then yes they are correct, those people will be saved. But if they mean saved from Hell, then no. People are going to go to Hell regardless of the time, Apocalypse or not, the only difference is now, billions of souls will be sent there all at once. So, Winchester's brothers, Bobby, and Castiel, you might be able to stop the Apocalypse (I highly doubt it) but you really can't save any one's soul, they have to do that for themselves.