Well this happened a month ago.

The muffler and cat-conv joining flanges corroded very badly causing them to separate. Thankfully though the muffler and the rest of the exh system was in good condition.
So went to mr.muffler (personal contact) and after $130 cdn tax-in (labour + parts), they cut-off the old flanges, then installed/welded new flanges on each side w/metal seal.

This is a standard repair and would certainly save you from buying a brand new and expensive exhaust $y$tem.