Hello, Im not sure if this an appropiate question for this forum as is not exactly mileage related but i'll post it anyway.

I have a ticket (Roundtrip Return), flying out of Frankfurt to San Juan, PR on
Aug 1. I will need to change this departure for a couple of more days (could be between 3 and 5). I just called the CSR and they told me that the earlier that i could leave is the 10th (which is not an option) and that is paying $200 change fee + $280 fare change fee since my fare is all sold out. I have not problem paying up to $250 and leaving on the 6th but the alternative the CSR gave me doesnt not work form me. I asked him about flying standby an he told me that was not allowed with my fare. I asked that what if I "missed" my flight and he told me that me ticket would be invalidated. Do you guys know if the standby thing is true? It seems unreasonable that if I miss my flight I will have to buy a one way ticket home. Or is there any other way around this.

Thanks all for your help.