What happened to Galadriel?

"No-Aragron's offspring would be classified as mortal, in the same way that Beren's
were. (Dior, Elladan and Elrohir were all mortal.) I think that the Valar decreed that
any being with mortal blood would and should be considred mortal, with the
exeception of Earendil, Elwing and descendants."

You are sort of correct.

Return of the King, App A., explicitly states that Elladan and Elrohir where born in Y. 139 of the Third Age - I find the concept of "mortals" with approximately 3000 year life spans to be a mite difficult to reconcile! No, Elladan, Elrohir, and Arwen were most definately given the same choice as Elros and Elrond.

But you are right in one sense: Elladan and Elrohir did *become* mortal, along with their sister, Arwen. I found that that is explicitly stated in App A of Return of the King (p. 389, I think) as the children of Elrond's choice was tied to when their father left Middle Earth - by staying rather than departing with Elrond, they effectively chose mortality.

Regarding Dior, you are probably also right - it is not really stated one way or the other, though it should also be pointed out that Dior died young at the hands of the sons of Feanor, and thus may simply have not lived long enough to be granted any choice in the matter.

Of course, Aragorn's children were definately mortal, though they may well have been very long lived.