Well you dont have to use focus. My macros look like this:

/target [target=Ðaria, nodead] [target=Ðixx, nodead] [target=Ðuxx, nodead] [target=Ðexx, nodead] [target=Ðaxx, nodead]
/assist target
/cast [exists,harm,nodead] feuerball

If my main dies Number 2 gets automatically assisted. Works nicely.
I have 4 mages and I use focus to sheep 4 different targets. Each mage gets his own focus and they all can sheep 4 different foci and fire happily away on there main target and resheep their focus with the press of a button.