It depends on your purpose, of course.
If you're role playing and you want to put the fire out, then yeah, you'll have to keep trying to put the fire out and when the role play is done you can stop.
If you're looking to get the mount, you got to put the fires out and take the dog to the temple and then use the diapason.
If you don't do anything, on the next server save the shadowthorn goes back to normal and you have to re-do the quest to make it burn.
If the world even is active you have to wait.
It's just the world of Tibia doing it's thing, there's nothing 'special' about it, it's a 'quest/story/lore' to get the Crystal Wolf.