just some assumptions here based on *nothing whatsoever*
you may not start the newly mounted engine without the paperwork done. you cant get the paperwork done without approved and signed off installation. you cant sign off on the installation without thoroughly checking the wing structures for damage, i.e. mag res imaging. you cant MRI the wing sections with the wing on the plane. you cant remove the wing in the goose bay hangar.....
ferry flight on 3 engines on with 4th under the wing for aerodynamics is the only option.. I suspect it will go straight back to the 'bus farm at LFBO...
for the ferry pilots probably one of the more memorable and interesting entries in their pilot logs.