He may go, he might not. I'm not sure you can read too much into him staying overnight. He was originally scheduled to fly to LA, so he has an extra day or two on his hands. Who would want to get on a plane, make the three hour flight and get home at midnight? Why not stay over, play some golf and scout some neighborhoods. If you're really going to be fair to the process, you've got to show some respect to the guys you're speaking with. He knew the terms before he got on a plane. The whole point of being down there is to get a feel for his potential new team, his role and the possible living arrangements. He knows Boston inside and out. He still may come home, make a list of the pros and cons and choose Boston. This is a guy that measures out his life by the teaspoon. So it's not surprising if he's really thinking through the decision.
As for a rift with Rondo, that was clear on the court. Rondo was lobbying for Avery in the starting lineup (in my opinion) because the team was just much better defensively and hustle-wise; and Ray probably was really p---ed off that Rondo didn't have his back. Ray was probably remembering how the Big 3 brought Rondo along when he wasn't as good as he is now, and probably feels a bit betrayed. KG and Paul? They're willing to sacrifice for the team, and they probably expect Ray to do it too. They also must have seen the change in the offense/defense numbers with AB in the starting lineup; and it just makes sense to save Ray's legs to come in when some of the starters go out ... rather than all 3 wasting their legs at the same time.
For his ego's sake, it's probably much easier for Ray to start over in Miami. Either way though, his role is circumscribed. In Boston he's competing for minutes with Bradley, Terry, and possibly Green and Pietrus. (Yes, I know Green plays a different position.) In Miami, he's competing for minutes (besides the 10 he gets backing up Wade) with Chalmers, Cole, Jones, and Battier (and yes, I know they play different positions as well). That's his competition for time on the court. And many of those players play better defense and make more hustle plays. So, I'm not sure what either coach is going to promise him; he's going to have to produce on the court, and there's no guarantee he gets the minutes.
The one irreplaceable talent he has -- late game heroics -- is the one thing both teams want, and that's why they're both desperate to sign him. He can be the difference between winning and losing a series in just a few shots. That's the bottom line.
We'll see what he does: whether he extends his legacy and fights through his changing role with grace, or whether he wants a fresh start. I think Miami's a mistake ... but his emotions might say otherwise.