Committed to taking on errand, he'll depart shortly (5)
I believe the answer is:
goner
'he'll depart shortly' is the definition.
(someone soon to depart or die)
'committed to taking on errand' is the wordplay.
'committed to' indicates a hidden word (the answer is trapped in or committed to the clue).
'GONER' is hidden in the letters of 'taking on errand'.
(Other definitions for goner that I've seen before include "One dead or beyond hope of recovery" , "He's unlikely to recover" , "Nasty princess" , "one with no future" , "Someone as good as dead" .)