I think the idea is rather simple in and of itself.

Add some visual effect for when a player reaches critically low on his health bar - the Knight could flash red, maybe have some sort of injured-looking animation when moving/standing, just something to maybe give players a quick visual que so that they would know a player is in danger so they can drop him a life pill or quickly help to defend him from monsters.

Even though I -can- look at the party members life-bars on the left side of the screen to see who is injured badly, it isn't something I think many people stop todo during the middle of battle...considering that you temporarily have to drop your own defense/awareness todo so..