This is probably not a bug, but in my opinion it should be considered one.

In one of my tribes two of my original villagers starved to death. I kept going, thinking I could resurrect them later, but of course their skeletons vanished long before that power became available.

I really think that if you have a power like that, there's no reason for the game to get rid of skeletons without the player's permission. Presumably, if the player hasn't had them taken to the mausoleum, then the player might be waiting for the power to become available.

Also, even if the game insists on getting rid of the skeletons, I think it's wrong to have them just vanish without a trace. They should at least go to the mausoleum (even if it's not complete yet). Isn't that what happened in VV3 and VV4?