Part of the catastrophic drop may have been google referrals. I've noticed in the past with old sites if you do a dramatic upgrade on them, google recoils a bit and starts re-indexing. i've seen search referrals take up to six months to completely rebound. The big shocker here is if google hits their homepage, it's met with a big "fuck you". I knew they were doing "shabang" but didn't realize they had zero fallback for no js.