Alternately, you could just have the destructible be targeted as something else. Unless this is a destructible that needs to be readily accessed by another type of unit, you can just have it be targeted as a wall or some other sort of destructible and have your hero be unable to target walls. I know this isn't a triggered method, but this way the unit won't even be able to target the destructible, which is what most units will do if they can't attack destructibles, so it looks more consistent with the rest of the game and it won't force the unit to stop its previous orders. Again, it depends on what the destructible is. If it's a tree and you still need it to be harvestable, for instance, I wouldn't risk it, but otherwise it might be worth a shot.
I just did a quick test of this with a Paladin and a couple of random destructibles, and it seems to work.