Leave on Christmas morning, possibly with papa (6)
I believe the answer is:
decamp
'leave' is the definition.
(decamping is a kind of leaving)
'christmas morning possibly with papa' is the wordplay.
'christmas' becomes 'dec' (Dec is short for December, the Christmas period).
'morning possibly' becomes 'am' (AM on a clock).
'with' means one lot of letters go next to another.
'papa' becomes 'p' (phonetic alphabet: alpha, bravo, charlie etc.).
'dec'+'am'+'p'='DECAMP'
'on' acts as a link.
(Other definitions for decamp that I've seen before include "beat it" , "scarper!" , "Abscond" , "Fold tents and go" , "escape" .)