How long should i hang on to storen?

currently have drew storen on my roster. i know he can one day be an amazing closer, but he does not have much value outside of being a closer and now burnett is closing for washington (standard yahoo 5x5 stats). there are not many options available on the waiver wire though, in terms of closers. but, as we know, it shouldbt take long before one is available. he's taking up a valuable roster spot so how long do i hang on to him?