Merida last year they decided they'd had enough and the body came away from the axle leaving 75km on one pedal and one spindle
The thing is you can tell when they are going to go as they have loads of play at the bearing end. A simple service (and maybe a new bearing if needed) will prolong their life a lot longer.
Ive got 2 sets of old mallets, find them much better than z-control or shimano DX ones as they are properly flat, rather than an spd with a cage, so give great support for DH stuff. Not sure about the new ones, im worried the pins would catch the tread meaning it'd be hard to unclip, i dont need the 'extra grip' im clipped in!