EC261 Question
 

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?

EC261 has compensation based scheduled arrival time vs actual arrival time, provided no extraordinary circumstances. You claim with the last airline after arrival at the destination.
Nothing to do with a connection- just arrival at the destination. Have not read that EC261 entitles you to a refund and a return ticket.

Many forums have master threads on EC261.
The BA thread is a good reference -->https://www.flyertalk.com/forum/brit...61-2004-a.html

The complete refund and free return to destination is called the "trip in vain" policy of some airlines. It puts you on the next available flight to your origin according to the ticket (and you don't get any FF credit at all). It's not part of EC261 and no, you cannot return to your origin six months later.

If you miss your connection, EC261 requires that you be rebooked to your destination by your airline at no additional charge; normally you should NOT buy a new ticket yourself. EC261 also provides for duty of care (meals and lodging) if there's a long delay for just about any reason.

BTW, the term connection requires that your flights be all on a single ticket/PNR.

It does appear that trip-in-vain type protection is included in EC 261/2004 (specifically, Article 8). But I don't know how much "give" there is in when the passenger must fly back to his point of origin to take advantage of this protection.

No way!

If the pax abandons traveling at CDG he/she will not get a full refund. The ticket will be repriced to a o/w GVA-CDG before any refund is processed.