I'll just mention some 'headcanon' of mine (not
headcannon). Coil's power is very good precognition, of the future based on if a certain decision is taken or not. He only actually gets the information on the option he doesn't take, and he gets it delayed so he gets it in 'real time' alongside the real timeline. Now my headcanon is that his precognition is only good for short term use, up to a few days or a week at most. So I theorize that if he doesn't 'end' a split for a long time the 'precognition' timeline gets more unlikely and stranger until he's finally 'killed' by something ridiculous.
Day 1.
Timeline A. Coil has Cheerios for breakfast.
Timeline B. Coil has Frosted Flakes for breakfast.
...
Day 15
Timeline A. Coil goes to work as consultant at the PRT.
Timeline B. Sudden unseasonal snowstorm causes traffic jams.
...
Day 30
Timeline A. Coil stays in hidden base.
Timeline B. A crash between a gas tanker, a milk tanker, and a grocery truck somehow leads to outbreaks of custard rain across Brockton Bay.
...
Day 60
Timeline A. Coil sees a therapist.
Timeline B. The weather starts off purple with hints of angst, although later in the morning a cold font brings a deluge of dubstep. Coil dies after confusing one of Bakuda's bombs with a hemorrhoid suppository.