I will keep it brief.
I HATE sad endings. Hate them. If I catch a whiff of an unhappy or uncertain ending, I drop a drama or movie like a hot potato.
With this one, I didn't even care. No, it's not a "happy ending," but it's not totally depressing, either.
This is the best zombie movie I've ever seen, and I watch a lot of Walking Dead and have loved World War Z for a long time. This tops it.