I had a similar thought to Valerie (great minds think alike!
{yeah, and fools never differ!!}
). It would be more of an issue if referrals were dying off.
I'm not really sure that a person is considered to be dead (at least legally so) just because there is no sign of them for a given period of time. I think that there has to be a determined effort made to ascertain their whereabouts before an application can be made for them to be declared legally deceased.
It could be a simple case of the individual having made the choice to become a recluse.
Besides, as long as you are getting the benefits of ClixSense it doesn't really matter where your sponsor is, or what they are doing!