Does Silver Lining negate a creeper requirement?
Normally, if a player has a creeper in play that player cannot win even if they meet the requirements for winning.

If the requirements for winning also require 1 or more creepers (such as in the War=Death goal) the player can win if they have those creepers, and must have those creepers in order to win, however if the player also has any other creepers (such as taxes) in play they cannot win. In this case, a player must have Death and War, but must not have any other creepers in play, in order to win.

The Silver Lining card only removes the requirement that creepers prevent the player from winning. It does nothing else to the creepers or to the requirements. So if you have a goal: War = Death, you can still win if you have War, Death, Taxes, and the Silver Lining card is in play.

"You also need the potato" places the requirement that the baked potato must be one of your cards in addition to the rest of the requirements in order to win. When that card is in play you cannot win without the potato, and you must have the potato in order to win, regardless of whether or not the silver lining is in play.

Ultimately, when a creeper is part of the requirements for a goal or a win condition that creeper in that case does not prevent the player from winning by achieving that goal regardless of whether or not there is a silver lining.