I've read through many pages of posts on other forums now and just don't know what to think.
The most likely scenario still seems to be that he had an accident or was harmed...perhaps as a result of being alone, at night, and possibly under the influence.
But one of the main police officers who investigated Brian's case and, perhaps, Clint (via his lawyer) both seemed to believe he was still alive. His girlfriend at the time and brother also seemed to hold out belief that he was or at least could be alive for some time, although their opinion seemed to waiver over time. If all of these people who know him and know the case best saw a voluntary disappearance as plausible, there must be some reasons to see it that way.
But disappearing voluntarily? Does it add up? If someone was trying to stealthily slip away from their life, it doesn't seem like they'd do it on a night where they'd been drinking or in the city full of witnesses and cameras. So I guess he could've either been unusually calculated and plotted the whole thing or he had some sort of emotional or psychological breakdown and fled impulsively, without planning, but then just decided to stay away permanently. The only other explanation--which seems like just ridiculous odds--could be he had some sort of psychological break down, such as dissociative fugue (where trauma can make you temporarily forget your identity and wander). But if that were the case, it still wouldn't explain how he made it out of the bar undetected...or how someone still didn't recognize him given how publicized his picture was.
Some notes on how he got out of the building: The police officer who worked on the investigation said they pored over the surveillance video and accounted for every single person. They would identify a person coming in and then find where they left in the footage later. They accounted for everyone, but him. They also brought cadaver dogs to the building. It turned up nothing. One lady I read said years later, the way surveillance at the location worked, if the security guards focused the camera in on one person to investigate something, it might temporarily lose other people's movements. So did he somehow get hurt in the construction site, did he leave normally and just unintentionally evade the cameras, did he use the back employee exit, or was he forced/carried out...
It's hard to imagine how this could be solved after so many years short of someone--possibly Clint or even Brian--answering the public's pleas for answers. Can anyone address whether some statutes of limitation could've expired, which might make it easier for someone involved to be more open now? Is there someone out there who could prove they know the answers without providing their identity and send an anonymous letter? This case circles and circles without answers.