There recently was an article that discussed about what the Dutch could do. It came down to 3 suggestions:

1. Building a dyke across the Waddeneilanden (killing off the entire waddensea but also protecting the rest of the land)
2. Raising up the existing dykes and sacrificing cities and villages that are nearby the sea since the dikes really need to become much bigger.
3. Giving up whole parts of the Netherlands, building floating cities and relying on higher parts of the country to expand and rebuild there.

What it is going to become, I don’t know but it will be really interesting!