If the belt tensioner pulley lets go, you may lose the radiator or fan assembly. In fact, you are lucky the idler did no damage.
I make it a ruile: Belt and idler every 3 years or maybe 30,000 miles.
Tensioner around 80,000 miles. I have 70,000 now, did my Graphites' at around 90,000 when it started to make weird noises.