Ah... I wasn't even refering to
Finwe with my comment. Didn't mean to get things complicated.
Aside from the two mentioned in
the Silmarillion to stay in
Mandos until the end,
Finrod says in
Morgoth's Ring that
Aegnor will stay in Mandos until the end.
I ment the published Silmarillion (should have specified),
the one that we all know, so I was refering to
Feanor, and Miriel.
Sorry I could not address this sooner. Though I knew about Finwe case, I had not read it myself. I don't like to answer questions who's answers I have not read for myself directly from the book.
But I just read this all tonight, so here goes.
In short, the only way that Finwe could have a second wife is if the Union with his first wife were undone, and this could only be so because Miriel would remain in Mandos forever.
It was actually written and can be found in Morgoth's Ring that after Finwe died, he chose to remain in Mandos forever so that Miriel could leave it.
Further, it was upon meeting Finwe in Mandos that her greif was lessend and she then spoke of a desire to use her body again, and Finwe suggested that Mandos might let her go if he would stay, and Mandos allowed this.
There was a Statute of Miriel and Finwe made because of this case, and there is interesting debate among the
Valar that went along with it. It was an intelligent conversation (a daresay it pushed my reading level), and so far as I know, for some of the Valar, the biggest chunks of dialog that can be found. They debated about why Miriel died in
Aman (among other things), as far as: was it
Iluvatar's doings and a payment for the great Feanor, or was it because of
Arda marred, and a thing which would be turned into good use.
As for Aegnor, his brother says he will go to Mandos and remain there until the end. He does not clearly state why that is, though it is implied, but still open to interpretation I suppose.
It is my interpretation that as Mirabella suggested, he would not find happiness. This may have been in part because he thought that Andreth herself would not find happiness, and not just that he would have to exist in bodily form without a spouse.