Not Really. The diode is probably the most reliable device ever invented and I have never had one fail in 20 years. Can they fail - yes! But invariably because their limitations have been exceeded, large spikes on the supply rail can take them out. But your Rx is full of small signal diodes, so if this happens you have bigger worries.
I always at least double the voltage and current requirements before buying diodes as these are simple devices that are small are very chaep. Don't skimp.
As for A123's I have not had a single problem with them so far. On this basis I could say I will save money and just fit one battery.
However, for me I look at it like an insurance policy. I really hope my wife doesn't need to pull out my life insurance policy, but it is there just in case one day she does....
We seem to have some crystal ball gazing going on here, based only on personal experience, and taking no account of wider experience or what might happen. It is up to each individual, but I prefer the peace of mind that my set up provides, based on wider experiences over a modelling lifetime.
I have had cells go short circuit (I am describing an internal short with in the cell to avaoid any confusion) and crash a model with a single battery. With Nickel based cells this was a common mode of failure and it has nothing to do with gradual cell degradation. I have also suffered a cell going open circuit. This is very rare but it happened to me, again in the days before I relied on twin batteries.
I have witnssed a fire caused by a shorted switch harness that would not have happened if there had been a diode in the system.
So I will continue to fit diodes in the hope that I never need them.