If aircraft are too late as per the contract and miss performance? Of course an airline can cancel. They are being smart and rebidding before canceling.
The A330NEO was sold as low risk and with earlier delivery slots than the 787. I'm sure many vendor contact clauses were violated.
It is not good to miss promise. Contracts must be maintained by both parties. Generally when penalties start to exceed some value, either party may exit the contract.
You are aware there is no way the A330NEO will meet EIS ETOPS requirements?
We are also in an era where aircraft are oversold where a 20% cancelation rate is expected.
There is also no way A339 financing requirements are being met. Leasing companies are avoiding widebodies due to more rapid loss of asset value. Combine that with poor outlook for A330NEO resale, as is true of all poor selling aircraft. Look at the 717, WN had to subsidize DL's leases!
Thus I have trouble imagining how AirAsiaX wouldn't be able to renegotiate their contract or cancel it.
Commercial aircraft sale / purchase agreements generally include a 'get out of jail' clause valid until around 18 months (less for NB / can be more for WB) before delivery (linked to purchase of long lead and customer specific items), which coincides with the time when serious money (or guarantees) change hands for each aircraft (or tranche of aircraft).
Although the contract may be treated as unconditional, the magic clause, is '............subject to financial terms satisfactory to the customer'. Sometimes the customer changes their mind, and requests those providing funding, to withdraw the funding offer, or increase margins.
In those circumstances, A & B may provide their own funding, at the original offer rates. Or if there are truly underlying credit concerns (or aircraft margins are already fine, or there is another more profitable order pending), the OEM may decide to 'let the order lapse'.
The WB financing market is at two polar extremes at present - blue chip and the rest.
Add engine issues (which even the 777X has already), and financiers are proactively turning the taps off or down, encouraging customers to moderate WB acquisitions. And blue chip customers can see the soft demand, and want to re-negotiate existing orders.
Buybacks are very commonplace in the vehicle leasing and rental industries, from light cars to heavy vehicles. Airbus has more experience with buybacks, and not just with the two most well known model ranges. Will they be quite so keen this time, when the engines could affect resale interest and residuals? Will RR have to join the party? Do RR have the desire and capacity to fund ownership on this scale?
Boeing will have to join this party for the 777 (they already have for the 748). Expect Boeing Capital to own and fund many 777's from circa 2020.