He states that he's talked to her several times about it. By saying that their communication hasn't been "healthy or open" or that they haven't worked on making a plan... you are just writing your own narrative of what happened. You weren't there.

Sure he can try plans, chore charts etc. When that doesn't work because she's lazy and a mooch and he gets so resentful he doesn't even want to look at her, try this. This approach is what actually works, in real life, when communication doesn't cut it.

In my first major relationship when this happened, I tried communicating for years. Resentment built up to the point we broke up. The second time this happened in a serious relationship, I tried communicating for so long, and when it did not work, I tried this approach - stop doing his work. He came to me and said "I feel like we're not a partnership anymore" and I responded "If you want to feel like we're a partnership, you need to act like it. Start contributing." Problem solved.

I'm not sure what your aversion is to him simply not doing her work anymore. She's not acting like they are part of a partnership, so why should he when it's at his expense? Why should he have to deal with the festering resentment of being exploited? That kind of resentment actually causes prolonged elevated blood pressure, which long term leads to chronic conditions like heart disease. Why do that to himself for her, when she can't be bothered to wash a dish or cook dinner?

I fully know the feeling of having your health deteriorate from being with an inconsiderate SO who doesn't care. All I suggest is that he stop letting her make him feel that way with her actions. He's not doing anything to her. He's simply choosing to STOP letting her effect him. If she wants things to go back to being a partnership, all she has to do is choose to contribute. It's really very simple. The day I chose to stop being a slave for an inconsiderate partner, I felt like I had a weight lifted from my back. It really is incredible when you learn that not being a doormat is as easy as saying 'no'.