I was told by my airline...... Not having a standby Captain at LHR is a commercial risk and the company is aware of this.
In this VS case this risk failed and cost big money.
In such cases my airline sort to grab any rated Captain travelling as passenger to operate and failing that any suitable inbound Captain, gave him 9 hours minimum rest at the hotel rather than his more normal layover time and required him to operate the delayed flight SAP.
When min rest was the case you were often legally rested but often were very tired and stressed and certainly in no mood to handle any extra extreame crap such as declaring yourselve unfit to fly and not having your contract renewed.
When a pilot has been jerked around for several years by cost effective rostering and has had his life and any attempted social and holiday arrangements blow to hell on many an occasion he generally becomes all the things he disliked in his senior Captains when he was a Fo.
I do not know the facts in Captain Cooks case but if they were approaching the above circumstances I have been there and have a certain understanding for the backround build up.
All covered as a "Communications problem by our Captain who has been spoken to by our management."
A management that knowingly engineered the no standby Captain risk situation.