User blog comment:Victory awaits/The actual outcome of Apocalypse?/@comment-92.26.159.59-20161002103841

I think that Lucifer's (initial) plan in the Apocalypse would be to kill Michael and in doing so force the remaining angels to bow down to him as he took control of Heaven, and from there nothing could stop Lucifer from gradually purging the Earth of all trace of humanity in his self-proclaimed quest to restore the planet to its pure, natural state.

Lucifer said to Michael that they "didn't even know the answer" when they were at Stull Cemetery; indicating that for all the angels' insistence that they WOULD win the fight and turn the Earth into Paradise, as far as the two archangels were concerned, this was one of their Dad's tests and all that they knew was that one of them would kill the other. Now, while it's true that Michael is older and likely a bit stronger than Lucifer, assuming that that meant Michael was certain to win the fight if they'd both had their true vessels; would be like assuming that a wrestler who has 500 lbs of muscle is certain to beat a wrestler who has 490 lbs in a fair match.

Also, Castiel didn't say that Michael would still be stronger than Lucifer if he possessed Adam instead of Dean; his exact words were, "it's not perfect, but it's possible." This could mean that Michael stood a fair chance of beating Lucifer if he possessed Adam, but it was no longer a certainty if Lucifer were possessing Sam.