Gravekeeper's Servant + D. Fissure = Force shield?

Hey, while i was dueling someone this came up to my mind, cause i had gravekeeper's serrvant and D. Fissure out, and my opponent said he could attack. I don't think that's possible cause dimmensional prison removes the card from play so in gravekeeper's servant it says specifically that it needs to be send to the graveyard. So my opponent can't attack.

Is this a true fact?

your opponent cannot send a card from the top of the deck to graveyard because their are sent to out of the game.
the card says: "Your opponent cannot declare an attack unless they send 1 card from the top of their Deck to the Graveyard."

so if he cant send a card from the top of the field, he cant attack.

Servant creates the state that your opponent must send a card to the grave to attack as a cost. When you can't pay the cost you can't perform an effect or in this case, an attack.

Since you can't confirm the top card of the deck even d-fissure and not only macro cosmos prevents your opponent from attacking at all with this card.