Dieing and being returned could cure the feeblemindedness.
Global enchantment Gift of health can cure affliction.
Fairy queen, aeroscale priestesses and a tienchi hero can cure feeblemindedness(only on living being).
The Chalice artifact works also.
Death, even when feebleminded, would lower all the pretenders magic paths by one. In some cases, it might be worth it, but the more paths you have, the more you lose.
Molog listed the mundane and magical means of healing afflictions, although I think Fairy Queen or Tien Chi heroine might be able to heal undeads' afflictions... I'm not entirely positive, though.