I think at 100,000 it's hit is lifespan according to the books. If it is a pain then replace it when the coolant leak is being fixed.

That being said I have never had a serpentine belt fail unless something else was bad too. Like has been said they are tough. I have run them with wear on the backs and cracked ribs underneath for years and they did fine. Would I tell anyone to do it, no, but on my car and I have the ability to swap it out in a few minutes I often place my bets and roll the dice. On a clients car I suggest they replace them when they look worn or cracked.

It has been my experience when they fail there is something else wrong. If it jumps off or shreds it is usually a pulley out of line or a bad bearing. If it jumps, replace it. It usually stretches the belt in an odd way and damages the internal belts in the belt. They have belts like a tire and like a tire with bad belts it will be short lived in this world.

Hopefully it won't cost much to fix.