A couple of days after telling me the time of the return flight had changed, Jetstar emailed me yesterday to say the whole booking had been cancelled. The first email offered a cash refund rather than a(nother) voucher which was on offer with yesterday's email, I'm sure you can guess which one I chose.
Flying down with Virgin. Flight times have changed a couple of times so I should be able to get a full refund if we are locked out of Tasmania.