hennebeck said:
If an evil goblin pleads for his life and the party takes pity on him, now what?
Depends on the goblin. They have personalities too you know.
Some examples:
Lawful Evil + Courageous : Goblin returns to its schemes, but feels he now owes a big favor to the party which he will honorably redeem.
Lawful Evil + Cowardly: Goblin volunteers to be a party members faithful (if somewhat despicable) retainer.
Chaotic Evil + Courageous: Goblin plots revenge.
Chaotic Evil + Cowardly: Goblin flees as far away from the party as possible before returning to his former ways.
Chaotic Evil + Cunning: Goblin volunteers to be a party members faithful retainer - but plans on stealing some good stuff and fleeing at the first good oppurtunity.
Should an adventuring group ever leave an evil goblin to live?
Depends on the group. Does the group tend to good, neutrality, or evil? In general, I'd say 'Yes'. If a particular goblin is not known to have committed a particular crime, then the fact that the goblin is capable of committing a crime is no warrant of a death sentence.
How often should he be a reoccuring villian?
Do you already have a reoccuring villain? How compelling is the goblin in that role? If the goblin has a compelling personality and is viewed with a certain measure of respect, then he can be a reoccuring villain or foil.