Is it possible to permanently lose the contents of a treasure box or can you somehow return and redo something to respawn the box?
Treasure boxes have, and probably always will be, one time occurrences in the Final Fantasy series. Therefore, if you sell a unique item you will permanently no longer have access to the item (I found out the hard way with the bloody
The only exceptions to these are mini-games. Although I don't think any mini-game in FF13-2 gives a treasure box as a reward.
Another point to note is the
Only if you sell the contents ;) otherwise you'll be able to obtain them in any time line, unless it's already opened, be it in the future or past.
Hope this helps you out.