Depends of what kind of triggers they are.
If you remove a patrolling unit, it will be removed along with its patrol information.
If you remove a brown unit, its kill-touching-hero trigger will not work anymore, but the event will still be there just never fire since the unit it references is nowhere (still a memory leak, and i dont know if it is fixable)
If you remove a brown unit that spins in a circle (check out my
wisp spinning system), the game will keep trying to spin it, even though it was removed. You have to disable those triggers separately.
--3ICE