That has always interested me just as much as the show itself is all of the "who was contacted and got cut or declined" behind the scenes info for Survivor. In some cases a person not playing again ends up being good for them -- Sandra, for example, was cast for All Stars but failed medical because she was in bad shape after Pearl Islands. There was a 0% chance she was making the merge of that season let alone winning, and coming back for HvV instead obviously got her a second win. I know it's not mutually exclusive, maybe she still comes back for HvV either way, but I feel like her legacy is more cemented without a premerge finish in All Stars.
Another tidbit for that season was that production sequestered the starting tribes together at the hotel before flying out for film. That's how Rob and Amber are a showmance and ironclad final 2 episode 1 without the show really elaborating how or why it came to be.
