At 10 years both types of coaches are out of warranty and repair costs will be 100% the owner's responsibility. From posts on this forum you will learn that sometimes stuff happens, in spite of what we all believe. Occasionally a gas engine will fail, and occasionally a diesel engine will fail. The cost to replace a gas engine may be $10,000 but to replace the diesel engine may be $30,000. The same goes for a transmission replacement even tho it is less expensive.
As a coach ages, the possibility of a major repair decreases the value of the coach to the point where a major repair can exceed the value of the RV. This point is reached quicker with a DP than with a gas coach.