I believe SFR is on the "verified developers" list for Bittrex and if i recall i thought someone mentioned, if a coin is on this list, they are exempt from delisting but I'm not exactly sure. I've personally already moved the SFR i keep on exchange from Bittrex to Crypsty, as Cryptsy has a SFR/BTC pairing and is not threatening to delist, but that's just my personal preference