I don't think we have to retain Melky. Personally, i think he's going to get over paid. All his value comes in his bat and i think you can find the 2-3 wins more efficiently. Honestly wouldn't you rather use the savings from Melky + move the 5 million from Navarro and use that $ get to Russell Martin. I think you do whatever it takes to get Martin. Find a cheap platoon LF who can hit RHP and platoon him with Mayberry JR.
Obviously we can't be having platoons at every position so if we were able to get Martin i would be fine with running Gose out there every day in CF and using a platoon in LF. If Gose can even hit 80 wRC+ he would probably be worth close to 2 wins over a season with his defense and base running.