People get inactive for a variety of reasons, stuff happens in their life and they get distracted, or maybe they are like me.. I tend to visit forums heaps for a few months, then normally ill get sick of it and take a break for a few months and just pop in every now and then. Then ill get interested again and start posting heaps for a few months, then bored again.. spasmodic is my posting style.. but this is a personality trait for me where I get really interested in something and go full on then kind of wear myself out of that topic...
but in answer to your question, email really is the only way.