I don't think the run flats will be too rough honestly. I have them in mine. I can tell they are in there, but it's not enough to bother me in the slightest. I would still get a spare, at least the tire itself, maybe a used one. I wanted to get one but my old lady freaked out on me over $100 because nether of us are working since we just had the baby.
If you had a "spare", like you said, how would you or who would change it? Well, at 500#/tire, you'll need some type of lift or contraption to put in and remove the spare. If you have one at home, worst case scenario, you leave your truck on the side of the road and use a pick up with the help of a friend to bring the flat back home and put the spare tire on the rim and go back to the truck. That is if the run flat was destroyed. Eventually I'd like to put a winch, a small one in the back of my truck mounted to some steel brackets that can be bolted through the bed and ideally into the frame. Then taking out and putting those big tires in the back won't be as bad.