Not that I know sorry.
Code:
EVENT_EFFECT_CHANGED (number eventCode, MsgEffectResult changeType, number effectSlot, string effectName, string unitTag, number beginTime, number endTime, number stackCount, string iconName, string buffType, BuffEffectType effectType, AbilityType abilityType, StatusEffectType statusEffectType, string unitName, number unitId, number abilityId, CombatUnitType sourceType)
You'd need to check the MsgEffectResult parameter for "Faded"
Code:
MsgEffectResult
EFFECT_RESULT_FADED
EFFECT_RESULT_FULL_REFRESH
EFFECT_RESULT_GAINED
EFFECT_RESULT_TRANSFER
EFFECT_RESULT_UPDATED
You could also check the active player buffs and there was a parameter "canClickOff" in some function GetAbilitInfo or something like this.
If you are able to check if canClickOff was true and the abilityId is the same in the EVENT_EFFECT_CHANGED with EFFECT_RESULT_FADED, it "could have been manually clicked to fade", but mustn't.
Maybe ZO_PostHook the player buff "icons" in the character window so you are able to deetct that someone actively clicked with the right mouse button on them -> to start make them fade.
If there is no API function provided in the txt files which does this already somehow for you, I don't know if you are able to detect it properly.