Someone at work is letting their personal issues get in the way of their responsibilities, and it might be up to you to make them aware of it over the next few days. Give them one more shot to prove that they can handle what they're doing. But as soon as you start to see a slide, pull them aside and have a talk. You'll be doing them a favor by waking them up. And you'll be doing yourself a favor because if they mess up, you'll have to pick up all the pieces.