Then it's impossible for him to be immortal. Unless magical stuff interferes with that. What do you guys think? There was no real explanation as to how or why he is immortal, he just is, and as we know organisms can not be immortal, save some jellyfish but they have tons of nervous systems and stuff and I doubt Skaarl and his genome allows for things like that. Anyone got theories on this?
She's immortal and indestructible presumably on account of being a spirit. Specifically Skaarl's a drakalops; a desert wind spirit.
Skaarl IS magical.
In fact Skaarl was said to be a wind spirit
there are many different lifeforms that function differently even in way that we cant imagine but its clear that you dont have to be undead to be immortal
its an ethereal manifestation, even if you destroy it it will reform
uhmmm there ar eplenty of immortals and semi immortals being on the fantasy worlds. For example you have elves (that are practically immortal of old age), you have zombies (immortals but brain damage, damage over body carries on) vampires and werewolves (unless they use silver bullets, some of them can even regenerate) and dragons (which are technically not immortals but have a life span so large that they might as well be to us while still be almost immune to damage) I'm guessing skarls is some form of dragon itself.
Also, look at Dr. Mundo, he has almost impossible regeneration thru science, that science have to had come from somewhere on the nature (that is how much of our science is designed) so regeneration from fatal wounds is possible, couple that with a large life span and you get basally an immortal being.
Didnt´ they say that Skaarl´s existence is basically bound to the Noxian Plains, which is what makes her Kind of immortal since the only way to end her ( or other drakalops, if there are any) would be the end the entire plains which is Kind of impossible unless Sol is bored
Probably after fusing with the crystal, he is no longer organic, and is fully made of magic crystal. If he kept being organic, it would be a matter of magic because of the crystal itself, so that would also explain the immortality.
The second one is the most comon in Runeterra, like 
or even Skaarl and the Yordles
