Identifier: DiplomacyMission
Event: A diplomacy mission has completed
Exports: nc_character_record, character_record, faction, region_id, character_type, target_faction, mission_success_level, target_religion

Identifier: LeaderOrderedDiplomacy
Event: A Faction leader has ordered a diplomacy mission
Exports: nc_character_record, character_record, faction, region_id, character_type

The latter event doesn't export mission_success_level.

I still fail to understand what could be the success level of a diplomatic mission except for the basic ones as it's very easy to make a deal acceptable.