wow that's an interesting question. Ive treated many folks with dementia and Alzheimer's during my time as a paramedic. really only your doc can answer that. Forgetting to do something on a rv can have expensive consequences.
However Ive seen folks who have had little to know change in their behavior for years. Other diseases changed their lifestyle before dementia did. If you and your wife think you have some good years yet to travel then get out there.
Like the others have said have an exit plan for the sake of your spouse. If things get bad just get off the road and into a facility that has a great memory care dept. meds and therapy can make symptoms much easier to live with. Make sure she is provided for as far as selling your rig and getting suitable housing. Good Luck.