Bulk barn or supermarket stuff seems to last several years. When (if!) it gets dry
you can revive it in warm alcohol (rum, brandy, Marsala, sherry) or throw it out. I've had small containers in my fridge for three years or so, and it's still usable. (A lot of it is bulked with coloured candied squash, by the way.)
Good-quality, real candied fruit, like the big chunks or whole candied fruit you can buy in Europe, is best for about a year. Then it starts drying out and losing the fruit flavour. I just used some in a panettone, and it was definitely better last year, fresh from Italy.