Planes are not like a car running an ESC. I've never seen the scenario you describe (leading to dead receiver).

First, to be concerned about draining an 1800-2300mah LiFe, you'll have been flying for quite a while. I've been flying a DLE 20 powered 70" Revolver on a single battery setup for 3 seasons now, with big digital servos on everything. It's been proven to fly 7 to 8 flights between charges routinely, and this plane is generally flown pretty hard. Not something that's just going up for a few laps with some touch and goes thrown in. Because the 2200 mah genuine A123 is not being pushed hard at all with this setup, it's generally charged every other outing. That why I suggested an 1800 might be plenty for your application?

Second, if the battery voltage were to drop into dangerous territory, the ignition module will put the engine into "limp mode" causing the engine to loose power, but it will STAY RUNNING, enabling you to land with the engine running! Going around may be a little dicey though....

Third, these optical switches also demand a solid signal from the receiver telling it to maintain power to the ign. module. If, for whatever reason, that signal is lost or erratic, the switch will shut your engine down. Your receiver at this point, should still be on line.

My point is that if you end up with a dead receiver in the air due to a low/dead battery, the engine will have quit long before that. The battery sizes I've suggested should allow plenty of flying time, and, the setup I'm suggesting is a popular one, often used up into the 50cc class planes.