A sensible consideration, but if the question is "what does FAR Part 25 actually require?" then a very literal argument could be made that incapacitation of a single pilot is not in scope.
The relevant text is found in Appendix D:
The following are considered by the Agency in determining the minimum flight crew under §25.1523:
(b)(10) Incapacitation of a flight crewmember whenever the applicable operating rule requires a minimum flight crew of at least two pilots.
If this is the only remaining issue to be addressed, then the provided workload mitigations will have established that "at least two pilots" is never required. Since that was a condition for considering incapacitation, it need not be considered.
Now, I assume that if anyone actually
tried such an argument the FAA would opt for sensibility and reject it as a consequence of sloppy drafting rather than the intent of the regulation, but I found it interesting anyway.