Just one person's experience, but my Lycoming pump failed at 340 hours. Certainly got my attention! But I had about a mile of altitude, and the engine restarted and continued to run on the boost pump.
The autopsy didn't show any obvious signs of failure, as far as torn diaphragms or any mechanical linkage problems. I offered to send it back to Lycoming, but they said don't bother. Which was a little puzzling to me; thought they'd want to dig deeper and look at failure mode.
I didn't bench test it afterward, but I think the failure was caused by a faulty check valve.