I have been told by the rtw desk of AA (2 different agents at two different times) that if you dump the rest of your itinerary, they will charge you the full price for the segments that you have used. As far as using them at a later date, there is no problem, as long as you finish the routing. I almost did this to get home from my trip later in the year, but decided not to since I don't know what will be happening with me later in the year/early next year.