Expires 06-07-2017, but ticket can be bought for any date in the future before then. Also, according to the VX FAQ, the credit apparently can be extended for one more year:
http://virginamerica.custhelp.com/app/answers/detail/a_id/512/related/1All credits are good for one year after the date they were issued (unless otherwise noted). You have until 11:59pm CDT on the date your credit expires to use it for payment. You don't need to fly by your credit's expiration date. If you book a flight using your credit, you can continue to make changes or cancel your travel plans.
In this instance, a new credit will be issued, which will be valid for another year.
