Non-qualified pilots look away.
Well played the FO. Fuel and weather being sound, then home base was the right call. Many many more lives than the CM1's were at stake, and single-pilot operation of a biggish public transport jet is a rare occurrence.
Sim does NOT nearly prepare one for this, although obviously it permits the usual rehearsal of drills and the actions.
Now think of a mid-Atlantic (winter) incapacitation of a crew member. And an aircraft full of people. The other guy's life is important, but not to the extent of risking 350 others. And the decision-making and actions are tough. No field within 2 hours flying time. Weathers at possible alternates tricky.
This FO proved himself more than worthy of progressing to the next stage. Be that present-type command or long-haul.
Would folks without experience please not contribute? Their questions are not valid.