Interesting one. So according to these myths, Ragnarok had already occurred before the 1220s and been less than all-destructive 
"Then the earth sank into the sea, "
... in the low countries, that can probably be said to have happened a few times. Logical local adaption of the myth. Heh.
What is most interesting is that this tale doesn't seem to be linked to Ragnarok at all. Donnar was killed by the Winter Giants. That's all. Woden still flies around leading the wild hunt for all we know.
And yeah, they do sink into the sea a lot. The whole map of Zeeland is totally different than it once was. Massive floods killed thousands back in the 1950's. Some things got swallowed up, others got uncovered.
Holland comes from the words "Holt Land" meaning there used to be a lot of trees there. Supposedly, the elves taught them to "turn trees upside down" to make dams and dykes.
Happens often enough that it's not considered a world-ending cataclysm around there. Unlike among us Norse on our mountaineous spits of land.
So how is the world prophecied to end in the low countries, then?
Book of Revelations I guess. They didn't have a Snori Sturlasen to write the stuff down. Scandinavia has the unique factors of a) holding onto pagan lore until they were well Latin literate, and b) having their own written language while they were still pagan.
Still, it is Snorri that gives us the earliest and best information, and it shapes our understanding of all Germanic myth. I think the Dutch didn't have the fully developed story by the time they converted.
Not to offend anyone who is a pagan, but the stuff was pretty much all made up. They were still in the proccess of writing the story.
So, long story short, I don't know. Most of what is known about paganism in the lowlands is contained in anti pagan sermons of the missionaries. Remember, they are Celtic too. Their versions of myth is a combined Nordic-Celtic mixture given a coat of Roman paint. So all three traditions got kinda muddled together, and by the time the people could read and write they were all Catholic.
I like the idea of the gotterdamerung having already passed. The old gods are dead, kinda like the old Death of Pan story.
Nah, dragon slaying is a well-established pastime of ancient heroes.
Cadmus slew a dragon before founding Thebes (and from its teeth sprang a race of fierce warriors; they fought and the last five survivors became the founders of the noble families of the city), Jason slew a dragon who was guarding the golden fleece. Perseus slew (in fact, petrified, using Medusa's head) a dragon to steal its lunch (i.e. Andromeda). Hercules slew Ladon, who guarded the garden of the Hesperides (though Ancient Magic tells the story a bit differently, if I recall correctly).