No they aren't. They're always killed. Ganon was killed in ALttP, TP, and TWW. Anyone with simple knowledge would know that. Don't even dare question it, Ganon was indeed killed many times, and revived many times also in the series.
Uh, no, if you had any idea an actual experience of it, you'd know that the world wasn't destroyed. It was recreated by the dragon. You can even get some dialogue from many past characters thanking you for all your help and giving kind words towards you, showing that pretty much everyone is still alive on the new created Earth. Including Claus most likely.
One of the most heart-warming moments in the game, honestly. A very satisfying end.
Ridley was killed in Super Metroid, pretty much, hate to break it for ya. You can even find his fossil in Metroid Fusion iirc.