There are some old friends I haven't heard from for several years. I'm not sure how to react. They may of course be dead. On the other hand they may just be disinclined to keep in touch. In case that is so I'm reluctant to bother them with frequent messages, as that would be rather like stalking.
I've decided to continue to send my annual letter at the end of the year, but not to send any other communication unless I hear from them first. I recommend that policy to others.