As long as the seams on your roof are still sealed and no cracking there, you roof is probably ok. It wouldn't hurt to give it a good clean and then treat it with RV roof conditioner. (assuming yours is the rubber roof type).
Regardless of what the nay-sayers argue, the roof does need to be cleaned and treated every now and then. The conditioners have UV protection and help put a thin layer of protection between the "rubber" and the elements. You put wax on the sides of your camper, why not treat the roof with stuff that's designed to help protect it too and keep it healthy?
I would not replace until I saw a tear or a hole or a spot so thin, you could see the wood under it. Treat it with an RV roof conditioner. It's the least evasive and may remove your anxiety.