I don't know your water chemistry, but while L copper is thicker, M should still be okay for a very long time in many locations. CPVC is okay for water lines in the house, but PVC generally is not, especially on hot supply lines. I don't claim to be up on all available technology, but I haven't heard of relining copper water supply pipes. There are techniques that can reline drain pipes. I'm not sure I'd want them relining my water pipes even if they could...it would decrease the size and reduce max flow rates and be problematic on any valves in the system. Note that cpvc (or any plastic pipe) will be considerably smaller in ID than copper, and you'd probably notice that decrease in flow when doing things like filling the tub, washing machine, kitchen sink (well, maybe not since many of those have restrictors). Unless there is a history of failed copper because of water or soil conditions, I'd leave it alone. Now, if the work was sub-par, regardless of the material, you'll have problems. Note, any copper run under the slab should have any joints brazed, not soldered, and it's best to not have any joints there at all. With CA's propensity for earthquakes, just movement could cause leaks if the pipes weren't layed out properly with proper movement accommodations. this would be true for both cpvc and copper.