I have only been in that position once; in my very first tournament at a casino. When it got to heads up, the other guy's wife came up to him to say they had to go to the airport. I was ahead 3-2 in chips, and this guy proposes a 50/50 split, and was quite arrogant about it, saying he was the better player and deserved it. I smiled politely and said "no thanks" to the split. This forced him to play more aggressively, so I just folded my bad
hands, which ate into his time even more. Eventually, he called for the floor manager and explained his situation, again trying to get the 50/50 split. I remained calm, and suggested that if he had to leave now, he was entitled to only second place, which he reluctantly had to take. I do not think I did anything wrong, but I probably would have split 50/50 if he wasn't such a jerk.
By the way, my first tournament was my only win....11 years of nada since then.