There's no right or wrong answer to this decision. It's a personal thing with a dollar comparison.
Granted, diesels, if maintained properly, will usually outlast a gas engine. They also offer greater towing and load limits over gas engines. But the initial purchase price of a diesel engine in any RV should be part of the justification for this statement. Also, have you looked at the price differences in gas vs. diesel at the pumps these days? Not so economical anymore when just comparing purchase price. In an RV, the living arrangement should be very important in your model choice. The engine would be foremost if you were going to be a fulltimer and running up a lot more miles given that is your residence wherever you make it.
Most, if not all the people in this forum (Georgetown) will probably not over challenge the engine performance as far as it's life for the time they have their motorhome. I'll bet almost everyone will max out their time with their car for mileage concerns before their RV.
Gas vs. diesel..........the decision will ultimately be yours!
Above all else..............