As a cabin crew who has dealt with this issue (happily, our pilot survived) the first thing the F/O did was establish control of the aircraft. He then called us to come and get the captain out of the seat to administer first aid.
His instruction to us was first to avoid hitting the controls and then secondly attend to the poor guy. (one outfit I used to fly for got us to actually practise this on ground with one of the flight deck crew as part of initial training. It was bloody hard to a) get a good enough grip on the guy and b) get enough lifting force to bring him out, clear of hitting anything. Airbus is definitely easier to deal with in this respect)
I'm sure you're all familiar with aviate, navigate. communicate. As soon as the first two were taken care of, we came into it.
I can only imagine how the poor crew felt and while single pilot approach/landing is a high stress/workload, imagine how it is when you've just witnessed your colleage dying/dead!!! Have a little sympathy!!
It was bad enough for us and ours lived to fly another day.
If fatigue is an issue, then it should be looked at.
Just wanted to add in from the CC point of view.