Thanks everyone for your kind comments. I spent about a month moping over the lost money, but honestly I don't even think of it anymore. I've since moved abroad and am earning more now than I did before. I've replenished the lost retirement funds (and then some) and my ER fund is back. In the grand scheme of things, this will likely be no more than a blip -- if that -- in my grand ER scheme.
Walking away from the loan, however, would probably stay with me much longer. I know some people have no choice but to walk. But I did have a choice.