I believe Rondo is completely devoted to his teammates and probably his coach - but beyond that, no reason to believe that his devotion to the Celtics/Boston is anything more than other players to their franchises.
He's not Pierce, who's been the face of the franchise for more than a decade and who has bought in completely to the Celtic mystique. Once he retires, Pierce will be showing up to sit with Mike and Scal for a quarter and do commentary. He'll hand out the Sixth Man Award. He'll remain an integral part of the Celtics community once he retires.
Rondo... I just do see it. When Pierce and KG retires, if Doc ever leaves, I'm not sure Rondo would push for a trade but I don't see him taking a hometown discount to sign an extension. But, I see him being 100% loyal to his teammates - as we saw in the first game against the Nets, sometimes to his detriment.