I think sometimes folks just take a break from these discussion boards for awhile... not a Lithium vacation, just of their own accord, wanting to spend a little more time on their own lives.
For some, this can be a busy season outdoors if they have crops to get in or gardens, lawns, and exterior of buildings to get ready for the approaching winter.
Some get very busy this time of year working up as many listings as they can get running, working to make those sales from here on 'til Christmas. Time is money, and they aren't spending much of it here, but are spending it listing inventory instead.
Sometimes just needing to take a BREAK from it here. While it's fun, and often good to help many who come here seeking opinions and advice of others, it can also be tiresome and even draining, and you can finally realize you're just giving too much of your time to a.... discussion board, for heaven's sake! And then you pay a little more attention and time to your own real life and family! 
I was thinking of him myself, one never knows if it is an illness or something else.
I will PM him or have Mr. C see if he can reach out to him to see if he is ok.
It is very unlike Dave to stay away this long 
