Model’s comeback cut short by arts institute (7)
I believe the answer is:
replica
'model's' is the definition.
(a model is a replica of something else)
'comeback cut short by arts institute' is the wordplay.
'comeback' becomes 'reply' (comeback in a conversation).
'cut short' means to remove the last letter.
'by' says to put letters next to each other.
'arts institute' becomes 'ICA' (Institute of Contemporary Arts).
'reply' with its last letter taken away is 'repl'.
'repl'+'ica'='REPLICA'
(Other definitions for replica that I've seen before include "Duplicate" , "Perfect copy" , "knock-off" , "Copy original" , "Parcel I made into an exact copy" .)