If taken care of the engine has lots of life left in it, maintenance is the key.
I bought my coach with just over 50K miles on 8 years ago, it now has 105K on it.
Even in the harshest of conditions if the engine is taken car of it will last a long time. I worked in underground mines. Engine life was not measured in miles but in hours. We could get +10K hours on an engine before rebuilding, which would be over 500K miles. This is in a very harsh environment. Keep the air intake in good working order, cooling system clean, and the oil changed and the engines are virtually indestructible.
2002 Monaco Windsor 38 PKD Cummins ISC 250 8.3L
2005 Jeep Grand Cherokee w/5.7 Hemi