I'd be more worried about the tensioner failing than the belt snapping. Most mechanics will tell you 5 years or 60,000 miles, whichever comes first.
At 80k and coming up to 6 years old i think you should look into getting the work done, just make sure they do the tensioner/pulley as well as the belt. While it's in pieces it's worth getting them to replace the waterpump too, since they'll have easy access to it at the time, they should only charge you for the part (about £30).