Can I continue a conversation with a client after the stay has expired and will they receive my message?

I wanted to send my client a message and some pictures after the scheduled stay so I navigated to 'past stays' and clicked on the conversation with my client. On the top of the page, above the text box, it says "this conversation is no longer active." What does that mean? Will my client receive my message? If not, then how do I start a new conversation?