I'm no expert but I'll give you my take.
I have a very small holding. If oil prices stay this low or go lower (which I believe they will), Virgin should be able to avoid losses in the quieter times of the year (the coming 6 months). If this happens then I think Virgins share price will go up. I think the decrease in share price is fuelled by the impressive results recently released by other airlines (QANTAS and Air NZ) and holders becoming impatient with Virgin (which is understandable) because they have not achieved as results that are as impressive. To my knowledge the international aspect of the business is still not profitable which is another concern.
If they break even for the remainder of the year EPS will be 1.3 cents per share, giving a PE of around 36.
Realistically they probably need to have EPS of at least 2 cents per share so they can pay out a modest dividend and keep on top of debt.
If oil prices go lower in coming months and share price doesn't increase I will be considering doubling up my holdings, however if no improvement has occurred in their next lot of results I will most likely sell and lose no sleep over it.