Article 19 of the Montreal Convention, which I quoted above, is worded very broadly to avoid the need to specific specific scenarios of losses. It covers the scenario you describe as well as many others.
Ah ok. So now s75 CCA 74 was a red herring even tho your legal advisor suggested it was a slam dunk
So instead you are now arguing your legal advisor told you that in the event of a flight cancellation you can claim under Art 19 of MC99 for any consequential loses, including any costs for an associated but separately booked trip?
Does it matter what the reason for the cancellation was? I am sure you (and your legal advisor) will be aware Art 19 has some qualifications around whether the airline is liable.
And lastly, do you know of any examples of any successful cases under Art 19 for this type of scenario?