Did complex C, or any at Mallard for that matter, have an incinerator?
And what was the medical ID bracelet for? This certainly sounds like foul play, but I'm curious if he was epileptic, had severe asthma was diabetic or had a heart condition? If you have a dead or dying drug dealer in your living room, you now have several problems.
Regarding the 40 minute wait. That's not unusual if there is a reception area in the apt building. Unlike a street deal, a quick visit triggers suspicion, esp in a hot zone where there is a lot of coming and going by nonresidents, so whoever he was going to see probably had a time 'policy.' Not being familiar with Everett, is it the type of place with police units patrolling housing parking lots, or ghetto birds making rounds?
Earlier it said he was a "small time" dealer, and I would agree with that. A "big time" drug dealer isn't going to an apt by beck and call via pager, an associate is going. For 2 grand in '91, if he did go himself, he likely not only knew the occupant, but had been to the building. If he didn't and was checking out a new supplier, he wouldn't go by himself. Which makes me wonder if the driver actually did stay in the car. If that driver saw or heard something, the police might keep it to themselves as it's still an open case and their goal would be to take down a bigger operation 1st and find Ben 2nd. Did Ben have firearms, registered of not? And were they accounted for? If one (or more) is missing, he was a) bringing a weapon that could be used against him and b) dealing with someone who he felt was dangerous enough to warrant bringing it.
Most (successful) dealers are not doing drugs themselves, but less experienced might, and that's a recipe for disaster in several ways. If Ben did partake, and the product was cut was something, he could have OD'd. Opioids exploded in the '90s, and most are familiar with the recent spate of fentanyl deaths. As long as there are drugs, there are ways to make them cheaper produce while exponentially deadly. If there is anyone still checking this thread that knew Ben, is he the type to stay and party with his clients? Because high people can and do fall off balconies, etc.
In the unlikely event he is still alive, any posts from his mother would be the way to reach him not while not expecting him to reply. The "we are safe" comment alludes to him leaving but is probably a mother's hope her son is alive. I'd imagine he had a lot of cash out of rotation for safe-keeping, but I doubt he'd take off on a February night in WA w/o it. Unless there was a plan after the Mallard to get it, or he literally escaped some situation at Mallard and took off. It'd be interesting to see if the driver could see all exits of the building. There is no doubt police know who rented the apartments, and that would still generate leads if the person living in one was not the same one on the lease.