To my knowledge,they ended up in Barry and cut up for scrap.
Not sure the Broad Gauge stuff ended up in Barry....certainly a lot of post Beeching locos did.
At first some Broad Gauge stuff was kept in The Works for preservation, but due to lack of space etc it was cut up, and recycled, a fate I suspect shared by the other beasts. North Star, of which there is a replica in the Museum, apparently has some original material.