What happens if i miss my booked train?

Basically, Im just wondering if i missed my booked return train from Oxford to Derby which is at 16:07, will i still be able to get through the barrier with the return ticket booked for Derby with that time later on, say around 6 which is where the next available train leaves for derby. I have bought a return ticket just to let you all know, or will it be impossible to get on a later train and i need to buy another ticket for that train?