If the rotor damage has swaged the rotor keyway tight behind the key, then it may never pull off. I suspect that you may still need to do some filing (or hacksawing) to allow the rotor keyway to open. See picture attached.
Alternator Rotor Key.jpg
Exactly, MartyNZ! This is what has happened apparently. Pulling didn't work as you have predicted, so the Dremel did the job. A very difficult job! The rotor is, however, finally out and there is no visible damage to the shaft, seal or the surrounding area (apart from the plastic flange in front of the alternator which has melted). The question about what other electrical bit might have malfunctioned still remains though, so a new voltage regulator will be on order shortly.
Thanks again to everyone for the input and advice!