[JASS] How to make Combat abilities?

[wikidme]

ok well im trying to make this combat ability like critical strike but instead the bonus damage is determined from your current mana. now i can get everything working but its buggy.

here is the spell (quite small)

function Trig_ManaStrike_Conditions takes nothing returns boolean
if ( not ( GetUnitAbilityLevelSwapped('A00R', GetAttacker()) > 0 and GetRandomInt(1, 10)<=4 ) ) then
return false
endif
return true
endfunction


function GetUnit2 takes trigger t returns unit
return GetHandleHandle(t,"caster")
endfunction



function ManaStrike takes nothing returns nothing

local trigger t=GetTriggeringTrigger()
local unit caster=GetUnit2(t)
if GetEventDamageSource()==caster then
call FlushHandleLocals(t)
call DestroyTrigger(t)
call UnitDamageTargetBJ( caster, GetTriggerUnit(), 0.5*GetUnitStateSwap(UNIT_STATE_MANA, caster), ATTACK_TYPE_HERO, DAMAGE_TYPE_NORMAL )
call QuestMessageBJ( GetPlayersAll(), bj_QUESTMESSAGE_UPDATED, ( R2S(0.5*GetUnitStateSwap(UNIT_STATE_MANA, caster)) + " Mana damage!" ) )

//call DestroyTrigger(t)
endif
set t=null
set caster=null
endfunction

function Trig_ManaStrike_Actions takes nothing returns nothing
local trigger t=CreateTrigger()

call SetHandleHandle(t,"caster",GetAttacker())
call TriggerRegisterUnitEvent(t,GetAttackedUnitBJ(),EVENT_UNIT_DAMAGED)
call TriggerAddAction( t,function ManaStrike)
set t=null

endfunction

//===========================================================================
function InitTrig_ManaStrike takes nothing returns nothing
set gg_trg_ManaStrike = CreateTrigger( )
call TriggerRegisterAnyUnitEventBJ( gg_trg_ManaStrike, EVENT_PLAYER_UNIT_ATTACKED )
call TriggerAddCondition( gg_trg_ManaStrike, Condition( function Trig_ManaStrike_Conditions ) )
call TriggerAddAction( gg_trg_ManaStrike, function Trig_ManaStrike_Actions )
endfunction


the problem im having is if, between the trigger triggering, i.e. when the unit is attacked, and detecting when the hit connects, the caster is told to do something else or the his misses for whatever reason (target blinks or has evasion), this trigger leak.

the point im making is, how is it possible to detect the hit NOT connecting and so delete the created trigger?