If you selected the option to delete the message and all replies then all messages are cleared from Nabble's records and there is no way for you or Nabble to recover the messages.
However, it is normal for Nabble to e-mail authors, sending them copies of any deleted messages. It is possible to use the text of those messages to re-post the messages, although, these will be new posts so the dates of the original posts will not be retained.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.