2017-10-05: Could we ever bring 'em back once they have gone

Continuing with the 'hidden' theme week, I'm thinking a hint is in order, though I suspect everyone will figure it out on Sunday if it's not guessed by then. I deliberately picked songs across a pretty wide time frame to demonstrate how common the unifying element is. It's usually, though not always, pretty subtle and yet it's not something anyone will miss once they know.