What does 'passing away of dhamma' mean in Satipatthana sutta?

Considering the definition of dhamma as given in this answer . What does it mean by '...arising and passing away of dhamma...'in the satipatthana sutta? Also, else where I read, 'all dhamma are also anicca' i.e. impermanent. Does the Buddha here mean that 'after few centuries the Buddha dhamma will be forgotten'? In what way does impermanence apply in regard to dhamma?