Usually that's modeled in the application layer. In scuttlebutt you'd store a higher-level state as one of the node-specific parameters. The gossip protocol doesn't need to know that you know the node knows it's about to die, though there are optimizations to be made there.

Despite what the sibling commenter claims, in a production system you absolutely need that distinction -- not in terms of the reliability of the low-level protocol, but in terms of the application features you want to expose. A node about to be removed needs a chance to drain active connections.