Virgin are still advertising vacancies on their careers board. By the time the vetting and interviews have been arranged for the potential candidates, Virgin Trains will no longer exist!!!
My point is that from what I have read and seen, the December change over will not make any difference to people in the recruitment pool so I would just relax and play the waiting game. I'm sure you'll get there eventually!
There's no harm in giving the HR people a bell if you've still got doubts.