Some people are okay with their hens and roosters killing their own. I'm not because that would just create a horrible scenario, where the first indication an animal was sick might be the fact that the rest are mutilating it, or have already inflicted fatal damage before I find out. They're so good at hiding illness or injury, often only the other animals know but the human can't see any signs.
Some consider that survival of the fittest, but domesticity isn't really about the fittest, we breed them to become dependent on us and more productive than they could physically sustain without our assistance, and therefore we have a duty of care which involves not subjecting them to avoidable harm, where possible.
But, it's all a matter of opinion, some people are fine with that state of affairs and would see it as the rooster doing you a service by killing an unfit hen. Theoretically unfit anyway, we don't yet know for sure what she died of.
Anyway, you know my stance on it, but I respect your choice and wish you all the best with it, even if you choose to keep him.
I would suggest you don't abandon or dump him if you do decide to get rid of him, because most domestic chickens, just like most domestic dogs and cats, cannot actually adapt to life in the wild. Only some do, and they breed so prolifically many people think they can all adapt just the same, but the survivors are the minority. Most dumped animals die, and not quick and merciful deaths either.
Doesn't matter how instinctive they seem in captivity; their instincts and physiology have
been bred to be quite different to their wild ancestors. They're usually nowhere near as parasite resistant, more susceptible to some diseases, they often don't have relevant experience about what plants are safe to eat, and their faulty instincts means the majority of them become predator food rather than survive.
They're used to food being provided, and a safe bed. They're bred to have heavier, meatier bodies compared to their ancestors so can't run or fly away as easily, plus it places a metabolic demand on them for fuel that their wild ancestors don't have to suffer under. They're too soft for the wild really. Some chooks go feral successfully, but they would be the minority, with the rest dying.
I understand it can be hard to cull them yourself. Maybe somebody would want him, if it comes down to you rehoming him. Maybe this issue will never happen again.
Good luck with him and your other chooks.
