Mark Jaquith made a “TLC Transients” method that you might find useful. Essentially, it implements a transient interface that does soft expiration and background updating.
https://github.com/markjaquith/WP-TLC-Transients
The idea is that you define a function to do the call that gets the data, then define the transient and pass it that function as a callback. When you make this call, it will get the data if necessary and return it, storing it in a transient for the defined time period. The “soft” updating means that it always returns the cached data immediately, and causes the update to happen after-the-fact, in the background (using a wp-cron job).
This would also have the advantage of always returning the “old” data until a successful update occurs. The way this is handled by his code is that you make your callback function throw an Exception if the retrieval of the data is unsuccessful for whatever reason.