Aahh... yeah, I don't know if there is much you can do about that sort of thing, beyond keeping very, very good records, and getting very good a dealing with ret*d insurance people.
I have found that working with a group of doctors/dentists/etc tends to help though. Then, even if your main dr/dentist/whoever leaves/retires/dies, the office itself is still up and running and maintaining your records. Of course, it helps that I live in a major metroplex. :/