A: Yes, all the cards are simply mixed together – it is not necessary to keep the treasure “buried”. Whoever gets the treasure map back after the mixup could choose “bury” any booty keepers he also received, once all the cards were all allocated, of course.
Naturally, if you feel it would be more thematic NOT to dig up your treasure to have it mixed up with the rest, you can institute a house rule whereby you set those cards aside, and give them to whoever gets the treasure map after the mixup. Just remember, as for all house rules, to make sure everyone understands the way you’ll be playing before you start the game. This prevents mid-game arguments.