Yes, he should have been able to hand fly the airplane. In this case he had some system failures, including autopilot, FMS and gyro/glass panel. Should have been able to handle partial panel in IFR, even with compounding issues, but sometimes things can overwhelm us.

I've got about 700 hours of single pilot time in a Citation II S/P and it's an easy airplane to fly, but when stuff starts breaking, like in the sim, it gets to be a handful pretty quickly. Most jets are flown with the Flight Director engaged about 95% of the time and with the autopilot engaged 90+% of the time, especially single pilot. Lot's to still uncover, did he have icing issues, pitot heat off?, spatial disorientation? We may never know the reason he couldn't handle it, but he couldn't. Very sad situation. RIP