Hi Mondrian,
Yes, I'm still here despite the morons' attempts to despoil out thread...
7a.  Fifty one in Roman numerals within a three-letter word for a spell [although that word can also mean a witch or a wizard] and is usually associated with voodoo.
11a.  Order of the British Empire followed by an acceptable abbreviation for 'island' and the standard cryptic crossword interpretation of 'worker'. 
6d.  Three-letter word for conclusion prefaced by a synonym for 'should' backwards will give you a word which means "a devil; a person driven by the most intense wickedness or hate; an addict or devotee" Chambers. 
I hope that will help.  I'm going out for a couple of hours but I'll be back to see how you've got on!
Kind regards,
Caravaggio