How much notice does and engine give you?

Have 950,000 miles on a 2006 Cat C15 single turbo. Like the truck and am attached to it. However I feel my driver and I deserve something newer to drive. Oil samples always come back excellent. I had it dynoed and it was 700 flywheel and 600 ground. Blow by test was 3.5" and was told that at 5" it is considered time for overhaul.
I could retire the truck for use on our farm (10,000 miles/yr. ) at which I feel it would last forever with out an overhaul in the future. Or do I try to get another 1-3 years out of it (we get 130,000 miles a year on commercial hauling) and take the chance of causing an overhaul to be done and then in order to get a persons $ back would have to run it for quite some time and not sure I want to have to drive it that many years. Truck is beautiful and I'm sure I could get decent money for it and have had many people "let me know if you ever want to sell it blah blah."
Anyway, if a person keeps running it does an oil sample start to show bearing wear or fuel dilution etc. in the oil and an overhaul is needed almost immediately or do you "retire" the truck then.

I guess I am wondering how long to run it and then save it for a back up or farm truck so I don't have to overhaul it. I hear all the time people run them to 1.2 -1.3 miles but they don't say what they do then ?! I want to drive something newer and not have to drive this one to get overhaul money out of it. I'm not afraid of the newer trucks. 2013 and on my friends have had great luck.