These consequences are largely not very restrictive. The goal is not to make unplayable characters, but to feel the violence of the fight (and then anyway, if they have a mutilation, that's because they were below 0 hit points, and they should normally be dead by the rules). Consider this as a saving throw to sacrifice a body part in exchange for life.
Severed finger : no effect
Severed foot : decreased movement of one level
Blind eye : -1 on surprise rolls.
Severed hand : no two-handed weapons
Severed leg : decreased movement of two level
Severed arm : no two-handed weapons, -1 Strenght and Dexterity point