Theres no reason why a rebuilt engine done right should'nt last as long or longer than the factory build.
A used block is already seasoned and preffered by big dog engine builders over a new block.
All the other parts have been heat cycled so many times that they are now dimensionaly stable.
The job just has to be done right, NO shortcuts!
Mine was still running strong from the factory (with only the water pump replaced) @ 96K. I didn't baby it so I'd expect at least 100K if it's done properly.