I'm not so sure this is over.
I have been involved in several management/union contract re-negotiations (elsewhere). The union's officials need to bring their membership along, to vote for the deal they've agreed. Twice in a row, this union has failed to do that, with their members voting against them (including during the current COVID crisis).
Last time common sense says the cabin crew would have voted in favour - Icelanders can be a strong-willed bunch.