Last year I was on a LGW-DFW-ATL award ticket when our DFW-ATL leg was cancelled and AA couldn't accomodate me on any other flights that day. They told me that the earliest I could confirm a booking out would be 3 days later and that award tix were not eligible for rule 240 reroutes. I called and spoke to an AAdvantage supervisor, who authorized a rule 240 endorsement in the record. Next morning (after a pleasant all expenses paid evening in the Embassy Suites courtesy AA), I went back to the airport and collected my flight coupons for TWA who got me home safe.