Water pumps are one of those "you never know" situations. I always replace them when I get a new to me vehicle - the one time I didn't, it failed in fairly short order. I knew better, and it bit me in the ass. It was my TJ! I replaced it with a Gates.
I've seen them go 150K miles, or fail at under 1K - and everything in between. Just luck of the draw I guess. My old MBZ got a new pump with the engine rebuild at 298K. At 315K, the pump grenaded - I never saw anything like it. The bearing was completely gone, the fan was wobbling around, yet it didn't leak any coolant. I probably drove it 50 miles like that before I knew there was a problem!