I had an issue where I had a high level fletcher but another unemployed villager had somehow taken over his profession block and he was not restocking. I added another block and he attached to it and started restocking. This happened again so I added another table and he seemed to be happy for a while. Then I went back and a low-level fletcher was occupying his block and my high level one was nowhere to be found. I checked the logs (this is a SMP server) and there's nothing about him being killed (though I do see where a couple of other villagers were killed in a creeper explosion about a week ago).