Back-up closers are valuable properties in all fantasy formats, but never as valuable as they are in AL- and NL-only keeper leagues where the cost of a regular closer at the draft approaches $30 and above. As a result, the closers-in-waiting find themselves being drafted for many multiples of the minimum bid i.e $8 would be 8 times the value of the minimum bid of $1. They are also protected from season to season at those salaries.
Those keeper decisions become more complicated when the reliever is entering the final year of his fantasy contract. His owner must decide whether to extend him for another year or so at the price of a higher salary. As an example, take a $7 Scott Shields. He can be protected at that price for 2007 but then goes back into the draft pool for 2008. Or he can be signed long-term through 2008 at the cost of an additional $5. His salary would then be $12 for 2007 and for 2008.
This decision is based on the continued belief that the reliever will actually fulfill his potential as a closer-in-waiting and close! It is this assumption that is the crux of the decision about whether to sign the back-up closer. If you still believe, then you are inclined towards paying an extra $5 dollars. After all, even a $12 Scot Shields will be undervalued if he closes.
However, I am inclined towards throwing back that player and redrafting him! How much is any middle releiver going to go for at the draft who is not currently closing? Does Scot Shields go for more than $12? If he did, it wouldn't be by much more than a $1 or $2, and the team would have him at that salary for three seasons versus the two the contract extension would have allowed.
This isn't a typical roster decision - keeping the potential closer and not signing him is - but it is something to think about.