Musical group departed with cover of Let It Be? (6)
I believe the answer is:
'musical group' is the definition.
(sextet is a kind of musical group)
'with cover of let it be?' is the wordplay.
'with' means one lot of letters goes inside another.
'cover of' becomes 'ex' (I am not sure about this - if you are sure you should believe this answer much more).
'let it be?' becomes 'stet' (I've seen this before).
'ex' put into 'stet' is 'SEXTET'.
'departed' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sextet that I've seen before include "composition", "Musical work", "band", "Music for six", "Piece for six".)