So I know that under EC261, if I miss a connection, I'm entitled to a refund and a return ticket to my origin.

The question is: do I get to use that return to origin whenever I want? For example if I fly GVA-CDG-DUB and miss my connection to DUB. Assuming I buy a ticket on another airline to get to DUB since there aren't any more flights that day and I need to get there. Can I use the PAR-GVA segment 6 months later, for example, or do I have to fly back on the first flight?