It's a bit harsh on the warrior but as far as I know there's nothing forcing you from keeping a warrior in the mob. You won't receive a refund! Depending on the cover situation they may become harder to hit when they are pinned and as such present a more difficult target than if they were still up. In those instances they can be skipped in favour of an easier to hit target. Pinned targets automatically escape from pinning if charged though and so can't be skipped. That sounds about right to me!