It's been 4 months and this thing is still running fine. The battery voltage is 2.2V, so I'm expecting it to run for another month or two. Also the code has been rewritten in assembly and now executes from RAM, though it still needs some polishing, I'll post the details in the next update. Disabling flash reduced the consumption by 25 uA and now the entire device consumes 19 uA, which means 11 months of battery life. I've also managed to find some better parts which should reduce the PCB size and power consumption even further. My current goal is 1 year of non-stop operation.