Hi
Sorry to hear about your fire - eek !
Only Fiat could tell you for sure, but I think it rather unlikely that removing the engine would be necessary. There is a small clearance all round the engine, and looms are flexible things so it should be possible to work round it. It may be the case that smaller items need to be removed to get access.
I believe there are multi-way connector pairs between the engine bay looms and the rest of the vehicle, so you don't have to thread anything through the bulkhead.
No doubt Fiat have a standard table of repair times for every item, which will be used by the insurance industry.