Wow, that's a lot!
Since you already put up a Craigslist ad, this might be too late, or you might not be interested anyway, but you can also pay a fee to extend your credits.
As mdh715 stated, SW is making some changes to the program, but I don't think they changed the rules about extending credits. Definitely verify with them, but I'm pretty sure that as long as the credits are all on one confirmation number, $50 will extend them for a full year.
I always seem to end up with just a few dollars here and there, so extending credits has never been worth it to me, but with $700+ I'd definitely pay the fee.