It will be interesting to see how this plays out.

From my understanding, EU261 is there to protect passengers from events which are in an airline's control, or which are otherwise in the ordinary course of business.

A pilot or crew member becoming sick is probably something I would consider as being in the ordinary course of business... not unexpected or completely unforeseen.

CX potentially has other options, including accommodating passengers on other flights (either their own or other carriers).

If we accept a pilot becoming sick away from their home port is force majeure - does the same apply to maintenance issues away from home base (for example where the airline in question may prefer to source a part from its own inventory rather than pay a third party?)

One pilot sick I think is foreseen. If two pilots became sick, that might be a different story.