Four regions of Germany that you can visit as a Disney family if flying into Frankfurt:
1. Drive south to visit the lovely Black Forest and EuropaPark on a 2-day trip. EuropaPark - the largest theme park in Germany - gets better reviews than the DLP.
2. Drive southeast (or take a train or an organized tour) to travel the Romantic Road all the way to the Neuschwanstein Castle - the inspiration behind the one at Magic Kingdom. Spend a day touring Munich afterwards for a total of 3 days for this trip.
3. Drive northeast (or take a train) to tour Berlin and then spend a day at the Tropical Islands water park south of Berlin. With travel, this trip will take you 3 days in all.
4. Drive north to visit Hamburg and then spare a day to tour the Meyer Werft shipyard in Papenburg. You should be able to see Wish under construction next summer on the shipyard tour. Plan 3 days for this trip.
You can, of course, do all of them on a circle tour if the cruise falls through. Even add side trips to Switzerland etc. - there is always more to see in Europe in the summer than what you can spare time for!