I hear it never rains in Florida.
If your ride goes down during your FP window, that FP automatically will change to be an open-ended FP good for the rest of the day at either that ride or a different ride (with restrictions). You should receive an email with details when this happens. That should not affect your ability to get additional FP at kiosks.
This link explains it very well:
http://www.easywdw.com/uncategorized/fastpass-replacements-should-yours-be-canceled/