It's frustrating as any caster when you're trying to cast on a target, and it gets killed mid-cast and you just lose the whole GCD. It'd be nice if, even if the target dies midcast, we still got the cast off: Why? Well, refreshing AF/UI, getting dualcast, not wasting Flare is all tied to a spell going off. You get nothing but a flat "Well too bad" if the target dies midcast.