Keep the DP and enjoy. 
Eventually the resale price will plateau and you'll have had many years of enjoyment.  The price will be low enough many folks will pay cash.  With good credit, there is always ways to get financing no matter how old a rig is.
A DP is built using commercial truck components.  These components are designed to provide a million plus miles of trouble free service.  
We tend to keep our RVs for 15 plus years.  Our current 5th wheel is 20 years old and we are still happy with it.  Not much has had to be repaired or replaced other than expected items like tires and batteries.  Preventative maintenance is the key. 
I hope to be able to keep it for about 6 more years until I retire and we get a new to us 5th wheel or DP to semi-fulltime in.