If I were you, I would place my bid and if you win the auction while you're away, message the seller NOW letting them know that if you win the item, you will be paying for it upon your return. They should be okay with it, if not, tough luck. Read their seller policies and buying rules if they have any.
eBay policy states that a seller can file an Unpaid Item case against you 48 hours after the end of auction. That doesn't mean they will...some sellers wait 4 days, some wait a week, some don't know that they can file a case.
