<font color="blue">I am not sure about the 'cascade' effect, Muhammad?</font>
In simple terms, there are two ways in which messages disappear:
1) User deleted
2) Moderator/admin deleted
In the case of the former, if there are no replies, the post is removed in its entirety---no trace remains. If there are replies, then the message is cleared, marked as deleted, and all replies remain. The reason for this is to maintain order in the database.
If a moderator removes it, regardless of whether there are any replies or not, that post and all replies if there are any, are removed.
In simple terms, there are two ways in which messages disappear:
1) User deleted
2) Moderator/admin deleted
In the case of the former, if there are no replies, the post is removed in its entirety---no trace remains. If there are replies, then the message is cleared, marked as deleted, and all replies remain. The reason for this is to maintain order in the database.
If a moderator removes it, regardless of whether there are any replies or not, that post and all replies if there are any, are removed.