Deleted Conversations

You have two options when leaving a conversation.

1. Accept future messages. Should this conversation receive further responses in the future, this conversation will be restored to your inbox.
2. Ignore future messages. You will not be notified of any future responses and the conversation will remain deleted.

You can retrieve it from your email if your Contact Details are set to "Receive email when a new conversation message is received."

Beyond that it's gone.