Black Mesa has a lot of nostalgic value for me, but it was removed for more reasons than the poison trap. When Highwon was considering a patched version made by Verified, it was decided that the map wasn't worth the large download required. There were the explosive barrels at the entrance, the secret area which caused delay due to free teleporters, and the actual map design, which promoted delaying due to its size and layout. Those are all issues unrelated to the levers, and I don't really think the map should be added again.
Actually - if possible. Rather than remove the levers... maybe allow anyone to turn it off. The poison only does like 1 damage every couple seconds.... so add a button at the bottom of the bunker or something to allow it to be turned off. This also gives incentive for innocents to actually enter the bunker.
The poison trap would be a dumb concept to bring back. The bunker is essentially the entirety of the map, with poison, you're left with just the outside of the map.
The only downside of the poison was because no one could turn it off. A simple method to turn it off - such as a little Valve you need to hit then boom. Free access again. That or just remove the poison entirely.
The damage is only minimal... Again it was like 1 dmg every 2 seconds or so. It's a VERY slow death. The time it takes to go from the top of the bunker to the bottom - max 15 seconds or so (I've yet to fully time it). You'd still be pretty healthy by the time you turned it off.