If under 1,000 Seacrest Serpents have been killed on your server the Guide NPCs will say "The Fire-Feathered Serpent is fast asleep."
When 1,000 Seacrest Serpents have been killed the message "Sleeping beneath the Oramond sea, the Fire-Feathered Serpent twitches and dreams of calling its children back" will appear in the server log or game window for all players. Also, the Guide NPC will say "The Fire-Feathered Serpent dreams and the earth is bleeding lava." When you ask them about this world change.
After an additional 2,000 Seacrest Serpents (or a total of 3,000 Seacrest Serpents) have been killed another message will appear in the server log or game window for all players, "The Fire-Feathered Serpent has awoken! Renegade Quara attack the sunken lands of Oramond!" Also, the Guide NPC will say "The Fire-Feathered Serpent is awake. Renegade Quara control the sunken regions of Oramond. "
This means Renegade Quara's will replace the Seacrest Serpents until your world has killed 1,000 of them then they will disappear and Seacrest Serpents will reappear with the message, "The Fire-Feathered Serpent goes back to sleep, beseeched by the blood of the Renegade Quara." I don't think any missions cancel the Renegades out, or at least I can confirm that completing the "Snake Charmer" achievement or fully completing the orb missions of Twenty Miles Beneath the Sea Quest doesn't make the renegades disappear in my experience. Also, according to Tibia Fandom when this world change is active you cannot complete Sub-Mission 1: Souls Lost At Sea.