Not successfully treated, a priest abroad died (7)
I believe the answer is:
uncured
'not successfully treated' is the definition.
(not cured or treated)
'a priest abroad died' is the wordplay.
I cannot really understand how this works, but
'priest' could be 'cure' ('priest' in French) and 'cure' is found in the answer.
'died' could be 'd' (abbreviation next to the year of someone's death) and 'd' is located in the answer.
The remaining letters 'un' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for uncured that I've seen before include "Still ill; not smoked, salted or dried" , "Not preserved by salting, drying or smoking" .)