The best you can do is to make sure your RV and vehicle is in excellent condition before your trip - tires, oil change, etc. You can't do any more.
Have some kind of roadside insurance in case anything major happens and they will tow you to the nearest repair facility for repair. Then you'll have to make a vacation out of waiting for your repair. We've never found a facility that wouldn't let you stay in your RV overnight while repairs are being made. Some roadside insurance allows for a rental car or motel, if needed.
During your days pack a cooler, your laptop, meds, books and whatever you may need and head for a park for a relaxing day. You can also go to the movies, museums, malls, area siteseeing, etc. If the repair facility knows you're not near home they'll most likely get to your problem ASAP. In our 16 years of full-timing and constant travel we've never heard of anyone truly stranded. Inconvenienced maybe but not stranded. :)
Bottom line - you'd get through it just fine. There are millions of travelers out there and many are going cross-country. You just can't worry about everything. Enjoy the trip even if it's cut short.