2. The Roc King
If the party raises the roc king to steal his feather he will only have 26 hp (1 hp/HD, as per the raise dead spell). If my player's go this route, is this the encounter intended for the glorious roc king?
You are correct, and I totally agree that this situation should be a little more climactic. A party of high-level adventurers with semi-loose morals would raise the roc king, beat his 26 hp into submission, and take the feather.
I can't change the rules for the raise dead spell, but I can make the encounter more climactic by requiring the party to make the same attempt to communicate with / soothe a living, completely healthy colossal roc: the queen.
When the party arrived at the pinnacle, they found the corpse of the roc king surrounded by a score of smaller (medium sized to huge) rocs - his children. When they noticed the party, they began screeching loudly, some taking flight, and one - the largest - hopping towards them with wings wide in a display of protective aggression. The party had 4 rounds to calm the alpha roc before it (and its siblings) attacked, with the creature getting more agitated and aggressive (raising the Diplomacy DC to calm it) each round. If not made at least indifferent, the roc children attack on round 5, mainly trying to grab intruders and drop them off the pinnacle. My players managed to calm them with some combined speak with animals and Diplomacy skills.
On round 6, concerned and enraged by the screeching of her children, the roc queen soars above the pinnacle, casting all in shadow. Here, the Diplomacy rules laid out for the king were used, with modifiers to the Diplomacy DC if the players fought / soothed the children, explained who the king's slayer was, offered proof that the slayer was himself slain (or at least was an enemy), offered to raise the king from the dead, etc. If made indifferent, she calms and orders the players to leave. If friendly, she allows them to raise the king, but does not participate in the encounter and might even attack if the PCs fail to woo the king and attempt to take his feather by force. If made helpful, she attempts to calm the king when he is revived, adding 5 to the PCs diplomacy check.
Then the players needed to win over the king as they did the queen. The only thing I did here is have the king refuse to simply give over the feather. Even if he sympathizes with the plight of the PCs and is made helpful, he is a proud creature, and demands that they best him in combat, meaning they can have the feather if they can take it from him. Once they grab the feather, the battle is over. The king respects their prowess and considers them friends.
Which all kind of sucks when the endgame is reached and the demiplane is destroyed. Poor roc king. And the rocettes.