I'm not organized at all about who I choose to follow. If I read something and I like the subject and the way it's presented and/or they write something I can relate too, I go look at their post list and see what other kinds of posts they have done and then I choose or don't choose. I don't unfollow a lot, but occasionally someone does a few posts that for some reason turns me off, way off. I may unfollow then. I don't give up on anyone I enjoy just for posting a thing here or that that is even to cra-cra for me..... ha... who knew there was such a thing?
I hadn't thought about how many dead accounts I might be following though, folks I started following long ago that are no longer here. One day when I think about it and have time, I might sift through just to see.
That seems a good way to go, checking their back catalogue as such. I think also, people change and that could cause us to follow or unfollow as well. I've seen a few people I follow write some things that I've not responded well to, but I tend to persist to see if it was a once-off thing before I unfollow.
You'll have to tidy up your follow list and eliminate all those dead ones some rainy day when there's nothing else to do.