Is it just me or I just realized that the reason why Antes still became the head in original novel was because Rosemary probably became the crown princess. The manwha clearly shows that the crown prince has an interest to Rosemary, that's probably why in the novel, Antes still ended up in the position instead of Rosemary. If that's the case, then that's probably better than thinking that the OG! Rosemary died or she was suppose to die in the near future.
"If there's a chance in the next life, you should come visit my library."