The computer provides a signal that modifies the advance for idle and
high revs, but I've paid attention to Lynn.  He's stated several times
that the rotary will run fine with a static advance of 25 degrees.  So
loosing the computer would not mean losing ignition.

That is accurate. The timing at the crank sounds substantial but is reduced by three at the rotor face. So starting is still easy. So long as the leading and trailing fire together or the trailing fires after the leading all is well. But never fire the trailing before the leading.

 

Loss of the trailing will cost about 5% power and can go unnoticed at less than full throttle.

Loss of the leading will result in a 20% loss of power and will be noticed.

 

On closed throttle, and at very lean mixtures, greater amounts of timing can be used, because very lean mixtures burn more slowly and mimic much higher octane fuel. And there will be very little fuel in the chamber at any rate.

 

The object of the timing whatever it is, is to arrive at the highest cylinder pressure at about 50 degrees ATDC. That would be about 18 degrees ATDC in a piston engine. So for good cylinder filling 20-27 degrees is good. For poor cylinder filling and or very lean mixtures more timing is OK. Up to 40 degrees. For boosted engines, where cylinder filling may exceed 100% or more, timing more like zero degrees leading and 12 ATDC trailing might be common. All depending on cylinder pressure. Still the max cylinder pressure at 50 degrees ATDC is what you are after. 

 

Lynn E. Hanover