How does the author use foreshadowing in Mockingjay?

Collins uses foreshadowing in the following sentence:

“'Of course you are. The tributes were necessary to the Games, too. Until they weren’t,' I say. 'And then we were very disposable—right, Plutarch?'”

In this sentence, Collins foreshadows the tributes' "temporary" value to President Coin. Everyone is dispensible.