I am pretty sure Monarch would not have had any cancellation fees, for the B787 order which was cancelled, this is because Boeing could not meet the delivery dates.
More like Boeing would have owed money to Monarch for failure to meet the contract signed.
Monarch has ordered all Airbus since they started operating the A320 and the only break with that was the B787.
The reason for the B787 was size, the A350 being offered was deemed to big at the time.
It is no secret that Monarch has looked at the NEO's, MAX & C series and we await the outcome.
For the time being, Monarch are taking delivery of new CEO's which are being leased from various leasing companies.
I would not write Boeing off yet, you never know what might be on offer, you have only to look at Easyjets history, big Boeing customer only to switch to Airbus.
As for A330 replacement, l believe the CEO said that once the narrow body order was finalised, they would then look at what to replace the A330s with.
Those who work within the Monarch Group may put me right or confirm what l believe was said.