What happens if you miss a return flight due to the first being delayed?

I am going on a very short trip to Rhodes and will only be there 6 hours. If the outward flight is delayed I could miss the return flight and the ticket is a cheap one that can not be transferred. It is the same airline both ways so for them to charge me extra to return when it is their fault for the delay does not seem right. They will no doubt claim it is not their fault as well if the delay was beyond their control. EG Volcanic eruption.