Co-pilot is essential for vital safety checks
WHY should it be essential to declare a Mayday and land as soon as possible when one of the pilots becomes ill or incapacitated?
A golden rule of commercial aviation is "expect the unexpected". Supposing something were to go wrong with the aircraft an hour later? Could the remaining pilot then cope alone?
Getting a stand-in to read the pre-landing checklists is vital. The introduction of checklists is one of the biggest single contributions to air safety.