Do you think I should just keep the board for backup parts?
Personally, I would probably end up keeping the extra motherboard, but I'm a bit of a hoarder. If you really need the cash though, then you're probably better off returning it. The decision will ultimately be yours to make.
Here would by my reasoning to hold onto it:
1) It's never a bad idea to have extra parts on hand. RMAs can take over a month and buying new parts for older hardware only gets increasingly expensive as time passes. Whenever I build a couple of new rigs, I try to keep all of their parts compatible -- ideally they'll all be identical such that if at some point in the future they start to break down I can still cobble their parts together into one good system.
2) If you decide to build a new rig in the future, you'll already have a motherboard. FM1 processors are still cheap (though who knows how much longer they'll be sold at major retailers...) and the FM1 motherboards use standard DDR3 memory (thankfully not old DDR2 -- prices are crazy!).
On the other hand, for $100 you could buy quite a few useful things. I guess this decision really hinges on how badly you need the money.
As for motherboards dying... I would say not very likely. Usually they're either dead on arrival or they're going to live for the life of your system. In some 15 years of building and maintaining systems, I've only ever had two motherboards die and I'm fairly certain that I killed both of them.
As for Corsair, good on them for taking care of you!
Probably about 90% of the systems that I build or own use Corsair power supplies and I've never had one fail. The same goes for Corsair memory and SSDs and now I'm even buying Corsair cases and keyboards... hah.
Whatever decision you make, good luck.
