On CNN just now, they listed possible replacements for Kennedy’s seat, and mentioned his son, Rep. Patrick Kennedy. Apparently the fact that he’s a legal resident of a completely different state, Rhode Island, is just a technicality.
UPDATE: And now they’re on to Caroline Kennedy Schlossberg, last seen being discussed for Hillary Clinton’s seat in the Senate from New York, and having been registered to vote there since at least 1988. What is it, if you’re a Kennedy and it’s contiguous, you don’t have to live in the state you represent?