As has already been noted in this thread, the large show building at the back of the Japan pavilion was built for the "Meet the World" rotating theater attraction, but was never used for that purpose. Instead, it was used for the lumber mill / carpentry shop for all of Epcot. I assume that's still what it's used for today.
No. The Biergarten was built as designed. As you face the Germany pavilion's clock tower, the arch to its left is the entrance to the Biergarten. The arch to its right (now Sommerfest) was meant to be the entrance to the Rhine River Cruise ride. Despite the often-repeated story that the show building for the ride was built, that's not true.
The ImagineeringDisney blog has an excellent article about this subject:
http://www.imagineeringdisney.com/blog/2012/2/17/rhine-river-cruise-mysteries.html