If this creature dies but leaves your graveyard before the next end step, it will remain in its new zone.

The “next end step” refers to the next end step that occurs, not the end step of the next turn. If this creature dies before a turn's end step (for example, during combat), it will be returned to its owner's hand at the beginning of that turn's end step.

The number of Zombies you control is counted as The Scarab God's first ability resolves. Players can try to change that number in response to the ability (perhaps by activating its second ability).

In a Two-Headed Giant game, The Scarab God's first ability causes the opposing team to lose life equal to twice the number of Zombies you control, although you scry only equal to the number of Zombies you control.