Is there such a thing then as a 20mm dia cutting disc that is held in a tool that resembles the front end of a bike - the wheel between forks? If there is I will buy it right now!
I hope you weren't thinking of a standard sized disc , as used in a Bosch type grinder!
I assumed that the normal use of a quality hydraulic puller and plenty of easing oil had failed.
I would prefer to use a 50mm x 1mm slitting disc in a 90 degree die grinder.
but a 1mm Klingspor slitting disc in a 4" grinder would be fine if you have access. A 1.5mm disc would generate too much heat.
As said I assumed normal avenues had been tried and the sprocket was being discarded.
Meanwhile off to Bottesford Egg Run with my shaft drive.
Heat and hammering should not be discounted: It depends upon what tools you have.