I expect Leonor will use de Borbon y (husband's familyname) for her children and in that order the Borbons would remain on the throne.
In Sweden Daniel became a Bernadotte so Estelle and Oscar are Bernadottes.
The Norwegian royals to the best of my knowledge don't use a surname so Ingrid Alexandra's children won't need one. It will be interesting to see what surname if any will be used for her brother's offspring.
Or they could use the belgian way and become "de España".
(After all, Q.Sofia adopted "de Grecia" and transmitted it to her children.)
Provided Spain would remaine united without a Catalunyaexit
I guess the same could be asked about Sweden, when Estelle will succeed, or Norway with Ingrid's children.
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