This is one of my Diet Coke drinkers who's eroded the facial enamel away from 2 year old composites on 8 and 9. Now the composites look like islands. Instead of replacing them the plan is to polish them so they're flat with the enamel, then refurbish the margins with a combination of Interface Ceramic Dentin and Enamel Primer, Surpass Universal Adhesive and Titan Flowable Composite.
The procedure is Clean and Boost for a few seconds to clean and etch the surface. Then on the clean and dry surface let Interface dwell for 10 secs and dry that. Add a couple of coats of Surpass 2 and dry, then a coat of Surpass 3 (and when the margin is really deteriorated I include a little Titan Flowable Composite). Now we can get a few more years out of these composites, assuming he really does cut out the Diet Coke (good luck with that!).