If you are meaning the "Herbst Spezial" (Fall Special) tickets - the promotion has been extended up to Dec. 2008 - they must be bought no later than
3 days before you are planning to travel. They can only be used on the exact train for which they have been booked, and as supermasterphil said, if your missing the train is not the fault of the Deutsche Bahn, then you have lost your money!
Good news is that the latest reports about the ongoing union and management "discussions" say that there probably will be no strike started next week. Wait and see! (Oh course, if they do strike, you would get your money back

)