As long as you take decent care of it, the bulk of the grille should last for a long time. If it has an enamel-coated wire grilling surface, that might get rusty and need to be replaced (especially if you've used a wire brush on it and scraped some enamel off); a cast-iron surface will last forever.
The most common thing to fail is the ignitor, but those are cheap and easy to replace, if you even want to bother.
The main thing that goes is the burner itself, but most of them tend to use one of a few generic designs that can be easily replaced from Home Depot, Canadian Tire, etc.
http://www.canadiantire.ca/search/se...=1335762566350