Ending a zombie story is a tricky beast. I'm thinking about writing one and am already worrying about how to end it (FYI, I don't even have character names or a solid idea yet, but I'm stressing over the ending). To my mind, there are only three ways to do it. Feel free to sound off in the comments if you think I'm wrong. I might nick your ideas if they're good, though!
1 - Everybody dies. All your characters, all the people who aren't your characters. Everybody. Dies. Or becomes a zombie, which is usually pretty much the same thing.
2 - They reach a safe place - military fortress, deserted island, whatever - and can live happily ever after with the dead banging on the doors but unable to get inside and start eating brains.
3 - Just stop. Pick a point and say "that's it. Done. Leave it there and let the reader decide what they want."
Normally, I'd say option one is the best, mainly because I'm not a huge fan of happy endings. Thing is, you can't really do it if you're writing in first person (putting in a stupid newspaper report or whatever at the end is just annoying - don't do it), and that's actually what I intend to do. The idea I'm circling involves letters, and who writes letters in the third person?
Option two is...well, that's not great either, and not just because I hate a happy ending. It's just so implausible that any place exists where zombies haven't gotten inside. Add to that implausibility that this magical safe place is also able to house people long term (I'm talking sustainable sources of food and water and whatever else it is that people need) and I think you're asking too much of your reader. Or thinking too little of them.
Which leaves us with option three. An ambiguous ending, done well, is a truly impressive feat. Just stopping a book with no warning or explanation or resolution...well, it's a bit of a cop-out, isn't it? Generally, when I read something that doesn't have what I consider to be a proper ending, I think it's because the author wrote themself into a corner and then couldn't think of a way out. I doubt that's true, an editor would have stepped in at some point prior to publication if it was (I hope!), but it does feel a bit like cheating. Unfortunately, it's the option I'm leaning towards right now. It just seems to fit the story if one day the letters just stop. There's no way of knowing what happened to the writer - if she survived the zombies or became one of them - and there's something about that which just feels right.
Also, I'm aware that "themself" is not a word and I do not care. It should be a word. In the same way that "irregardless" just sounds better than "regardless" even though I know it's not actually a word. While we're at it, it also bothers me that "habitable" and "inhabitable" mean the exact same thing.