A replacement loco being sent but no available path to get it there on time perhaps?
Cannot see any likely looking paths into Inverness (or out of Craigentinny). I'm not quite sure what options there are - other than fixing up 67003 (which is maybe what they're doing) - or if it still has ETS available, use a 66 for the traction with the 67 for the train heat?
The 73/9s had a difficult night last night and what I think was the only 'spare' in Edinburgh (73966) is currently running up to Aberdeen to take 1B16 as the loco on 1A25 this morning had issues (73968 IIRC). Interestingly it's scheduled to get there 2 mins before 1B16 is booked to depart, but then looks like it'll be waiting a while at Edinburgh anyway.
The Colas 47 is on an errand down in Doncaster currently, so that's not an option.
So realistically it's fix up 67003, or DB supply a replacement 67, but not sure where from at short notice. 67007 is up in Inverness, but on RHTT duties (3S95) and given a lot of current issues are due to railhead conditions, wouldn't be a wise move to pull 67007 off this.