You cannot stop your members from deleting their own posts, unless it is a topic-starting post that has replies.
To be clear, they cannot start a discussion and then delete it along with all of the other contributions, but they CAN delete a post they made in the middle of the discussion, and they can delete a topic-starting post with no replies.
Actually, I've found a way to ensure folks do not delete their postings, be they replies or topic starters.
Go to your WORDLETS at Eve Control Panel > Display Settings > WORDLETS tab... click the icon under EDIT... click the SEARCH WORDLETS tab... enter 'delete' in the WORD VALUE field and scroll down and click on the SEARCH button.
Read through the offerings... anywhere it says anything like 'EDIT OR DELETE' for members, change it to EDIT (only). For instance, the field titled RIGHT_DESCRIP_PERM_UBBX_1011, I changed to read 'Can edit own posts' and the field XSL_ALT_EDIT_DELETE_MESSAGE now reads 'Edit Message' on my board.
However... to get rid of the text that allows members to delete their own posts, find the XSL_DELETE_MESSAGE_QUESTION field and delete the text in the VALUE field... voilà! The option to delete one's posts disappears. Don't forget to scroll to the bottom of the page and click the 'UPDATE WORDLETS' button to put your changes into effect.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .