Perhaps if the database was not compacted since you have deleted your conversation you could try to copy the database to your PC and try to find your conversation using a Textviewer. You are still unable to restore the message, but you could read it and write it down on a piece of paper.

Perhaps look at you old backup. Open the comm_and_cal.zip, search for Root\home\user\.rtcom-eventlogger\backup.tgz extract from there el-v1.db and have a look at the content of this file using a File viewer (text or Binary Mode)

Please report if it has worked.