When the A2 drops out of regulation and goes into it's "dim incandescent" mode, it best not to fire up the lamp again at that point, as it is severely underdriven and very hard on the lamp. That's likely why yours burnt out.
Usually when I have a post talking about underdriving a lamp, a dutiful cpf member comes along and reminds me that underdriven lamps are not efficient and produce light that is very yellow. I'll reply that I don't mind the inefficiency, as long as I am getting a longer runtime (though with less total amount of light) on the same cell(s) and a lower light level, and the yellowing is actually nicer to what I'll call "morning eyes," the eyes you wake up with in the dark that hate bright light.
This is the first I have seen it claimed that underdriving a lamp is hard on the lamp. Are you referring to the A2 stock MA02, specifically with the incan A2 regulator (does this regulator have something to do with that), or all lamps, everywhere, always?
I have been using the same Tad Custom's A4812 with his E-socket in an Elite head in a single-cell setup with a 3.2V LFE18500 every night for at least a year with at least one extra cell swap a night. I'd peg the amount of light close to an E1e, about 12-15lm, but more yellow. I get about an hour out of these 18500 Duracell Solar cells with the A4812. That is at least 365 hours on this particular lamp, probably closer to 450 hours. What I have always thought was (no telling why), though not as energy efficient as when driven by proper voltage, and color temperature drops considerably, an underdriven lamp will outlast a properly driven lamp, and far far outlast a more efficient overdriven lamp, and my anacdotal experience supports this. But I'm only using Tad Custom's Xenon lamps.
Where did you get the idea underdriving lamps is hard on the lamp? Or are you, again, only referring to A2 and MA02?
I will add, if running incan A2 with secondary cells, as soon as the lamp drops out of regulation, the cells are empty, close to 2.5V, so do not use either the LED or the lamp at that point, but swap in fresh cells.