Begun to implement parallel info (alternate approach would be fine) for a History per player of chunks. (haven't run this on the server as it's unfinished and may not exist in this form, but I have the datafile as a copy of the player data file, renamed).
This is to work as follows: chunks are added parallel to the player info, chunks are removed parallel to chunks being scuttled and ceasing to be home chunks (it would require removing the chunk from all possible players) but chunks are NOT removed from the victim upon takeover.
Player should have list of all their current chunks and all those that have been taken from them at some time in the past. This list is what's checked when entering a new chunk. Entering a formerly owned chunk tells the player who currently owns the chunk they once owned. That information is only available to past and present owners of the chunk. That way if you build a base and you have levels and an anvil, you can always retake it even if you weren't online when the base was taken.
Only partially implemented. Needin' help with this one.