Suppose you have characters A, B, C and D. Suppose the 'focus' order is A -> B -> C -> D, so if A dies, B takes over, etc. This is a huge problem when A dies and B + C are on low health. In such scenario (which happens quite often) you actually want to switch to D, because he has more health and will live longer. By switching to the character that lives longer you will have to switch less and thus lose less time.

You will also have to add an "exists" check, because otherwise this setup will fail whenever you remove someone from your team to replace with a friend's character.