The thing is, your subscribers aren't really "dead" if they stop watching you. They could start up again at any point. This has happened to me before, when someone stops watching after a while, but starts up again. YouTube currently deletes dead accounts, so I think that's good, but I don't want them to become unsubscribed from me, because then they'll never have the opportunity to rediscover my content. I don't care about the number though, so if I lost them as a statistic but they still got my videos, and they were recounted if they ever open one, then I'd be fine with that.