decide 和 When and where to build the new factory 是动宾关系，所以，When and where to build the new factory 做主语时，谓语动词必须用被动语态。has not decided是主动语态。yet 常与现在完成时连用，所以，最好使用下面的句子：

    When and where to build the new factory has not been decided yet.