Yes, it will be fun!
I wonder whether your best bet might be to ask QF to check your bag only as far as LHR. Collect it there (you arrive at T3), drop it at T3 left luggage, do a landside transfer to T5 (Heathrow Express or Tube), do your LHR-DUB-LHR, go to your hotel and stay overnight. The next morning, come to LHR T3 in time to collect your bag before you fly LHR-DFW.