1. Not much to investigate, the cost of a new belt is so low it dictates that it should be renewed if removed. It would make sense for the tensioner to also be replaced at the same time. Any decent mechanic can do this and they would also check for mis-alignment.
2. Non guarded belts are not covered in the VW Warranty, clearly mentioned in the exclusions. They also refuse to cover any damage caused by an unguarded belt breaking.
