In my experience Event Handlers are a wonderful way to reduce lag. You just need to be careful that each one doesn't run a complicated script. That could cause problems. In this case all he needs to do is use a hit or killed event handler to set a the value of a global variable.
In my recent mission there are about 600 soldiers, almost all have three killed event handlers on them, and quite a lot have four. Despite that, putting a LAW into a truck full of soldiers has no noticable effect on lag.