I've replaced shocks on a nissan truck before after 50,000km (30K miles) that were not leaking oil, but were definitely at the end of their lifespan. When a rear shock was removed, it could be compressed, but it took my buddy and I pulling as hard as we could to get the shock to decompress to the normal length. Dampening - gone. Prior to replacement, the ass end of the truck would go all over the place from frost heaves or expansion joints on the road.
In my area, 50,000km is a good yardstick for OEM suspension. As others have mentioned, there's plenty of variables. It's a salty, snowy mess here for 4-5 months of the year. I'd expect a much greater lifespan in the desert.
but what I mean to underline is that I wouldn't wait for leaking oil to replace suspension components. Then again, I love buying shocks and tires..... It's a character flaw