What's your take on immortality through the use of magick in TES universe?

One of my quests has an immortal bro, who might or might not have the know how to bestow immortality on other bros.

Tell me why or why not is this and will through not work.

Only ways of immortality I know of are becoming a Lich, or vampirism. That or living in an Oblivion plane. Seems people don't age there.

Wouldn't mantling also be considered immortality, or would that fall under the realm of living in an Oblivion plane? A mortal mantles a Daedric Prince(CoC -> Sheogorath), or becomes a Divine (Tiber Septim -> Talos) and they are now immortal or is that simply a metamorphisis since they really aren't what they used to be?

I'd consider it a metamorphosis, but so is vampirism and being a lich. Just a lot more complex and hard to pull off, but I assumed he meant while still in nirn as a humanoid. There's also Corpus, but thats not around anymore, and you dont want that unless you happen to be the Nerevarine. And there's finding the heart of a divine and extracting it's power, but that ship has sailed.

It would be cool if lorewise the Dovahkiin absorbs so many dragonsouls that he gains their immortality.

Corprus puts the body in a permanent stasis, the Nerevarine and Yagrum Bagarn are the only ones not to get fully mutated though. Immortality is possible through magic as showed by skilled wizards.

Divayth Fyr became immortal/long-lived as well, apparently without the aid of necromancy.