I don't know what Brokie Fever is, exactly - but what I do know is that the movie industry is cynical, and that it's all about making the bucks, - and also that Gilliam has shown he's able to do decidedly un-classy things. (Ref. his diatribe against Michelle Williams). So I think the choice of that punchline does indeed deliberately reference Heath's death (and the way his role was "resurrected" by Depp and others).
Gilliam/the distributers/whoever is responsible for the trailer may even tell themselves that in riffing on the main star's mid-shoot death and in using the interest and attention the film gets specifically because of that, they are actually honouring Heath and his art. After all, it's a way to get more people come watch his final film.
But when all is said and done, I personally think it's about the money. They use what they have. Cynically. Or maybe just realistically.
The film itself still looks cool, though, all marketing ploys aside. That's the main thing.