All good answers above. It's possible BA or AA would keep you at LHR and put you on the next day's flight. There would be a choice of LHR-CLT-TPA all in one day or LHR-ORD-TPA which would get you in one day as well but try to request the LGW-TPA nonstop. Since you would be more than 4 hours later than your originally scheduled arrival, you each can claim 600 euros, I don't know the exact GBP's amount, plus enough to cover dinner and breakfast and drinks costs plus a hotel. When my GF and I had an 8 hour delay of a VIE-MXP flight, OS gave us a 20 euro voucher, so you should insist upon more. Your special meal will be probably be lost since that request most be made 24 hours in advance, but it never hurts to ask. Keeping receipts for anything out of pocket and remember to note the time you get off the plane because if you don't have much of a delay, it's on you to make the next flight if possible. 85 minutes is not alot of time to go from a satellite of T5 to T3, but it can be done. If your DBV flight was getting into LGW, you could request BA to change your ticket in advance to the LGW-TPA flight and you pay your own ground costs, which is something you could do delay or no if they still have room on that flight with the award and the right agent. There's a bus that will go from LHR to LGW and since you would need a hotel anyway at DFW, you offer to cover the hotel at LGW. With an award, you can do that now through AA. Same day changes are also common if you explain that you only have 85 minutes, at best, to make the flight at LHR. LHR and LGW are co-terminals so it makes sense to suggest it.