It could be coincidence that the feather picking began right after their flock mate died.
But then again, especially if this deceased hen was high ranking, it very well could have shaken up the pecking order to the extent that a lot of them are now facing new relationships with one another.
Usually, a shakeup in the social order gets settled with very brief confrontations that we humans barely notice. But depending on personalities involved, and the fact that feather picking may be stress related, a few may be "acting out".
The problem with not doing anything, letting nature sort things out, is that feather picking can become habit forming. Then you really have a long term problem to cope with.
My advice is to do everything you can to discover who the perpetrator is. It may be one or it could be more. Usually it begins with just one, however, and the others pick it up by being around the behavior. So you want to strive to break up the behavior so it doesn't become habit and spread to others.
I've had good luck segregating the culprit(s). Let them have a pen to themselves adjacent to the others so everyone is still together. If that's not possible, protect the victims with Blu-kote painted on the bare flesh. Or you can sew or buy saddle aprons to try to cover the bare areas.
A very effective way to retrain a feather picker not to do it is by installing pinless peepers on them. After a few months of not being able to focus on a targeted victim, often the behavior will stop and you can then remove the peepers.