Diesel life span

I am thinking of purchasing a one ton deisel dually. Currently I have a 250 gasser. Can any of you senior members that have been towing for years with a deisel tell me how many miles I can expect out of a deisel if follow factory maintenance schedule. Not asking any particular brand, just the engine expectancy. Trying to justify the cost!

Spend some time on the diesel truck forums. Some of the early Rams/Cummins have amassed over one million miles with the engine never taken apart. There still will be replacement parts for the rest of the truck and engine accessories, of course.