The way Humba, Mumbo, and all the other characters talk, they make it out like they had been inhabiting Showdown Town for awhile. Maybe LOG just placed them there and modified their memories? It is curious to note that in Banjoland it says something along the lines of "Tanktup's whereabouts are currently unknown". Where did he go? And he's so huge, I don't get how he could hide from anyone. Or get out of Bubblegloop Swamp. Perhaps Tiptup is with him.
As for Scribes, I believe they've permanently replaced it with "Mini-Scirbes"... apparently you fill out the form here: http://www.rare.co.uk/community
Also, it's interesting to check out the official Facebook pages for all the Banjo characters. They did little Q & A sessions and it's cool/funny to read their response's. (Here's Banjo and Kazooie's, for example.