Bitcointalk is not a company and a forum without traffic is not a forum, it is a relic or a ruin, like the Roman ruins that people visit, not a forum. If hypothetically tomorrow there will be no more traffic on the forum, it will surely continue to survive because it will not need money, but it will not be a forum, it will be a ruin.
It will always be a forum. For the sake of argument, I kind of see what you're saying, but its more like a museum than a ruin. The museum has a 6-year-deep layer of spam around it, yet its important exhibits are still easily located with the right Google queries.
I'm sure that Theymos is well aware that the traffic is being moved elsewhere in fact that's the whole reason he banned them in the first place.
Traffic isn't being moved elsewhere. Everyone who opened an account on altcoinstalks is still here. Organic traffic over there is minimal because its 100% spam... Like a contemporary museum without exhibits, there's no reason for visitors to go there.