You would have to take the bus to MGM and then transfer there to the Ft W bus.
FWIW, you will be spending quite a bit of time on the bus if you park at DD (and since Sundays are rather busy at DD, the shoppers will thank you for not taking up a parking place). There is no bus from DD to MGM (or any of the theme parks). You would have to take the bus to one of the resorts and then wait for the bus to MGM. Once at MGM, you would have to transfer to the bus for the WWOS. THe WWOS bus service ends about 7 pm.
If it were me, I'd park at the stadium and then drive to FtW. However since that isn't what you want to do, I'd either:
park at MGM and then drive to FtW afer the game or if I didn't want to pay for parking -
I'd park at FtW, take the bus to MGM / WWOS and back again. At least after dinner, I'd have the car nearby.
Best wishes -