"has long finished" is correct and can be used in written English.
Example: The movie has long finished, but I'm still thinking about its powerful message.
We've long finished lunch when the police turn up.
My brother and sister had long finished breast-feeding when I arrived, so I never longed to be held and bonded with in that way.
The world has long since finished having its Norman Mailer conversation, but few writers in their day received as much attention.
Trained… The world has long since finished having its Norman Mailer conversation, but few writers in their day received as much attention.
Work that should have been long finished has dragged on: a first contractor was replaced by Carillion – but then Carillion imploded.
You know what I mean?" He has not long finished filming The Hangover Part II, reportedly for a fee of $5m; he's keen to point out it's not a no-brainer sequel.
She has not long finished her first comedy, the David Mitchell and Robert Webb series for BBC2, Ambassadors, in which she plays the wife of the British diplomat (Mitchell) dispatched to the central Asian republic of Tazbekistan.
"Come on!" He and Jocelyn had long ago finished writing the title of the book on their lesson plans.
