Depends on who owned it and how well maintained it was, and lastly, whether it was a "Friday afternoon special" or not as to whether or not it will need it soon. I heard of one person that got 900k out of theirs before it pooped the bed, but several others were in the 650-700k mile range before dying.
Rebuilding, from everything I've been told (and I asked.....A LOT), is not worth it. Last quote I got was from Truck Country just south of Milwaukee was $12,500 for a 3/4 block. Mind you, that was at least 15 months ago, so figure the price has risen since then. A 3/4 block does not include turbo, injectors, injector pumps, nor manifolds.....or LABOR. I set aside $25k. All who I asked advised that having engine rebuilt was equal to or more expensive than just buying the block directly from Daimler (Detroit) that has a warranty, and an extension can be bought. That engine is a parent-bore engine (read=no cylinder sleeves/linings).
How about starting with an oil analysis to give you a rough indication of it's health?
Hope that helps.
