Can't really see Fitz leave Evanston (except, maybe if the Bears came calling some years down the road), but if Fitz were to leave for GB, his 1st call should be to Kafka to be his OC.
Heck, why not have some fun and imagine Fitz asking the Packer FO to sign Siemian to be Rodgers' back-up (would be a better option than Kizer).