I didn't blame Ray for leaving. Whether you want to admit it or not, he was pretty disrespected and under-appreciated here. Every year they tried to trade him. That final year they decided to start an unproven Bradley over him. They DID trade him and the deal fell apart. In the offseason they went out and signed Jason Terry and had plans to sign Courtney Lee even as they were negotiating with him. He had several issues with Rajon Rondo behind the scenes. Meanwhile, Boston lucked into the ECF (Atlanta and Philly in the first two rounds) and realistically was no longer a contender. Why bother coming off the bench for a fanbase that didn't appreciate him (I saw Ray ALlen trade threads on this board once a week), a GM that didn't want him (tried to dump him at least 3 times), a coach who undermined him (sticking him on the bench behind a kid) and a leader who didn't like him (he and Rondo clashed). You can't blame him.
Also the Miami/Boston "Rivalry" is severely overblown. They just happened to be the team to eliminate us two years in a row... I don't think of them as a "rival". It was a good situation for him. I'm not even rooting against Miami in the playoffs.
I'd be totally in support of him coming back in some capacity. Ray is a class act. Would be great for him to retire a Celtic.