It's not unexpected to have a few losses in a group of just-shipped wild caught bugs, I imagine shipping stress or parasites is a more likely cause of death than not having enough wood to eat at this point.
Earthworms and wood lice occupy the same detritivore role that millipedes do, don't they? Wouldn't that just generate more competition for food? The fruit peels is a pretty cool idea though. Have you had any issues with mites when you do it?
Neither earthworms nor isopods have any affect on the rate at which wood rots, furthermore, both are considered pests in a millipede enclosure. Earthworms are the last thing you want in your millipede tank. They will quickly consume your substrate and turn it into worm feces which is inhospitable to both young and adult millipedes. Earthworms also crush molting cells which can wipe out your entire millipede population if it's a species that molts concurrently. Isopods will compete with your millipedes for food and there have been reports of isopods eating millipede eggs.
For hastening the wood rotting purposes only. I was thinking that the millipedes are not yet added for this equation.