A ticket is 'just' a tool to confirm a reservation, a document that allows you to show your reservation at the entrance of the venue. You can therefore have a valid reservation without having a ticket. In such a case, you obviously retain the right to the booked seats. Beware of resold tickets. Here it is often the other way round: your tickets may have been forged and there is no reservation at all. Your ticket is then only a (worthless) piece of paper.