It would be a very manual process (a check-list of items?) but yes, you could probably spawn everything back in. It's something I have contemplated doing and when the time arrives I will probably "cheat" and reimburse myself for all of the stored items on the old file. Everything else can remain, regardless of how expensive or a pain in the butt it was to make.
There is one thing I will miss: A Nether Fortress 200 blocks from the portal that was made on almost perfectly-flat ground and was nice and open. Finding Wither Skeletons was a breeze on that thing.