Ascetic's last to leave German city (5)
I believe the answer is:
essen
'german city' is the definition.
(I've seen this before)
'ascetic's last to leave' is the wordplay.
'ascetic' becomes 'essene' (member of ancient Jewish sect).
'last to leave' means to remove the last letter.
'essene' with its last letter taken off is 'ESSEN'.
(Other definitions for essen that I've seen before include "German industrial city on the Ruhr" , "Krupp HQ (Ger.)" , "Industrial city of northwest Germany" , "Main industrial city of the Ruhr" , "European city" .)