1940 WI: Netherlands/Allies Hold onto Zeeland

1) Much of Zeeland is large islands off the coast of the mainland Netherlands. Could these islands be turned into a "national redoubt" and be held by the Netherlands and aliies for the entirety of World War Two? Could the islands be held against the Germans for that long? Would control of these islands speed of D-Day? Would it change the location of D-Day? What other butterflies could this potentially cause?
Basically the Channel Islands but bigger.
The Germans will take it eventually but at a high cost.
Every Allied soldier on that island is screwed, unless they call in another Dunkirk, which might end up like the Greek evacuation.
And the Germans would keep bombing Rotterdam and Amsterdam while the redoubt holds out.

So basically, it's not possible.