It should be a goal for Earth to send a probe to one of those stars. As the probe will be unmaned, a mission taking a hundred years or more is not out of question.
Unlikely, but possible (if the probe was really big or really chatty in parts of the spectrum we pay attention to). Tiny probes could pass by us without us noticing them I'd think, though if they needed to send transmissions back toward their origin we might pick that up.