Had a long drive to a cabin for the weekend and listened to another podcast revisiting Brian's case. Didn't offer much new, but I started to make a mental list of all the places he could've gotten out of the bar besides the escalator because there is video evidence that didn't happen.
Note that a few of these may border on absurd, but again I'm only listing every other possible place Brian could've escaped the bar undetected:
Service Exit
Located in the back of the bar for the band and delivery vendors to use, the exit itself led into a long-ish hallway where other businesses in the building's service exits led and down a hallway that came out of the building. There was no camera on the service exit within the UTS, however there was one in the corridor/hallway that led out and CPD said they did not see Brian in that video.
However, that video has not been released so public can't take a look so we don't technically know for sure if they missed anything whereas with the main entrance we know for a fact he didn't go out there because video was shown proving it. With it being nearly 1 AM on a Saturday, I doubt many people went down through that corridor though so I presume it would've been easy for LE to watch everyone in that hallway and not see Brian since there were probably very few of them that night.
Fire/Construction Exit
Door located just to the left of the main entrance to the UTS but off-camera of the security cams that caught everyone at the main entrance. The door was clearly labeled with a sign that said something to the effect of "Opening this door will set off an alarm", however per one of the girls Brian was talking with and the last people to see him before he walked off camera to presumably go back into the UTS, it as a 'well-known fact' that the alarm on that door either wasn't working or was shut off after regular business hours.
Since this happened very early in the AM on a Saturday, if true the alarm would for sure have been shut off. A slight contradiction to this one could be that Clint reported that he saw Brian back inside the UTS and he said he was "going to talk to the band" at which point he vanished and Clint never saw him again. It's possible he said that then went back out the main entrance and went through the fire exit. As far as why, could have been drunken curiosity or pure drunkenness in thinking he was going out a different way.
It's also possible because he was being openly flirty with the two women outside, he thought he'd sneak out and meet them in the parking garage for a chance to meet up with them later without arousing suspicion of Clint & Meredith who obviously knew he had a girlfriend. This exit also did not have a camera and anyone could've walked through it without being seen. The issue here is while there was construction going on at the time, LE and others described it as "light" construction and the part they were building was mostly done so it's not as likely that Brian could've fallen or gotten injured/died down there and nobody found him. LE said they searched that area and didn't find him either.
Off the Patio
The UTS had a small patio area outside on the second floor - see image on left side - and it's at least possible that Brian went out there and tried to jump/leap down and do whatever. Find the girls in the parking garage, just trying to do something dumb when drunk, etc.
This one is not very feasible because obviously that's a considerable drop with multiple obstacles and it's likely Brian would've been injured or worse attempting this. The bar still had ample customers at the time because they didn't close for an hour when he vanished and the patio was reportedly one of the most popular areas of the bar where it was packed and seating was limited. Highly unlikely Brian could've even attempted this without anyone seeing or reporting.
Through the Ceiling Tiles/Roof
I didn't say they'd all be realistic. The only other way out would've been to somehow wedge himself into a ceiling tile, possibly in the bathroom because anywhere else he would've been seen easily by multiple people, and climb up through to the roof. It's not know if the roof was even accessible through the ceiling but again, trying to list every other possible way to escape the bar itself other than the main entrance. I obviously do not think this happened at all.
The service exit or fire exit are the two most likely IMO because I think there's almost a 0% chance he was met with foul play within the bar and they had some massive coverup, etc. That goes against all logic in this case. I wish LE would release the footage of the hallway leading out of the service exit just to see if other eyes can make anything of it but I doubt that will happen.
From there, I think it's 50/50 whether Brian actually got out of the complex or was injured/died there and his remains are still somewhere in the facility. I'd believe either is just as likely at this point.