Diseased pretender...

[archaeolept]

Elixir of life may work; that's an interesting suggestion, as being "reborn" will sometimes get rid of an affliction.

It is also relevant what pretender you have. An immortal one you might as well kill (in your own dominion). An undead or demonic pretender will have the disease icon, but the disease will not affect them, so you can ignore it.

Other than that, either you need a unit w/ the "heal" ability (certain national units, like Arcos priestesses or others, or the summonable but crappy faerie queen), or the Gift of Health global, or (best of all) the Chalice artifact.

If you have none of these, or it is too early in the game, then a ring of regen will at least keep you alive, although it will not stop your pretender from picking up other afflictions.

I once had my immobile Baphomet flaming head get feebleminded by some cavalry he was teleporting on. I had to leave him drooling in the ditch for 25 turns until I managed to score the chalice.