If you gain control of a permanent, and you leave the game, the control-changing effect will end. Unless there's another control-changing effect affecting that permanent, it will return to its owner's control.

If you gain control of a permanent another player owns, and that player leaves the game, the permanent will also leave the game.

The effect of Dack's second ability and the effect of the emblem's ability last indefinitely. You won't lose control of the permanents if Dack leaves the battlefield.

The targeted player draws two cards and discards two cards all while Dack's first ability is resolving. Nothing can happen between the two, and no player may choose to take actions.

The ability of Dack's emblem will resolve before the spell that caused it to trigger.