What happens to the zaps?

If a person's wallet/node isn't up and someone sends zaps but the other person can't receive them (becuase their stuff is down), what happens to the zaps a person sent?

Are they stuck in some inbetween cyber-limbo? Or do they get a failed transaction notification?

Example:

Yesterday, I asked folks not to zap that article I posted. Today, I see Highlighter shows 24k zaps. Is that attempted zaps or did those zaps go somewhere? Will people get them back eventually because they didn't get my wallet/node?