It's impossible that you lost your whole world and everything. If you rejoined, and your inventory was reset, then that's truly remarkable. All whitelisting does is make it so others can't join, even if you got kicked for not being on the whitelist, your playerdata wouldn't reset. If your inventory and world is reset completely, I'm bummed, but if you had your inventory, chances are your base is still out there somewhere. Try restoring a backup, if you have one.