I've seen broken rotors before, and they usually baffle the tech for a while. Unless they blow apart completely, you get spark, although it can be erratic.
Even no spark isn't a sure bet for a busted rotor -- I'd personally check for a bad OVP relay myself!
My brother's Buick split a rotor once -- he was ready to change the timing chain when I suggested he check for spark first. Zip -- took the cap off and there were only bits for a rotor. Cheap fix, but took a bit to find....!
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!