Guten Tag, Arkadiy,
I think that its pretty obvious which one Lennon was going for in the entire context of his "dream". After his dream was reached, then perhaps your second nihilistic assessment would happen... but then we would have to move this to religion/metaphysic forum. FWIW, Lennon was a fan of Gogol and Lermontov. At about this time in his career he was reading "Fathers and Sons" (saw a photo of him with book in hand).
Imagine
Imagine there's no heaven,
It's easy if you try,
No hell below us,
Above us only sky,
Imagine all the people
living for today...
Imagine there's no countries,
It isnt hard to do,
Nothing to kill or die for,
No religion too,
Imagine all the people
living life in peace...
Imagine no possesions,
I wonder if you can,
No need for greed or hunger,
A brotherhood of man,
Imagine all the people
Sharing all the world...
You may say Im a dreamer,
but Im not the only one,
I hope some day you'll join us,
And the world will live as one.