Send message about dope disappearing (7)
I believe the answer is:
passing
'disappearing' is the definition.
(passing is a kind of disappearing)
'send message about dope' is the wordplay.
'send message' becomes 'ping' (to ping is to message electronically).
'about' indicates putting letters inside.
'dope' becomes 'ass'.
'ping' going around 'ass' is 'PASSING'.
(Other definitions for passing that I've seen before include "Overtaking" , "Short-lived - death" , "Ephemeral" , "Casual - death" .)