where is the rest of them?

While I don't know about Warwick, yes, Jarman passed away in the early-mid 1990s (AIDS-related, the technical cause of death, I'm guessing, was pneumonia, as it's probably the most common cause of AIDS-related deaths).

Unfortunately, a lot of actors only do one or two films and then "vanish", never doing another film again. This is for a lot of reasons, with the most common being 1) they were never offered any subsequent work, 2) they could not otherwise attain subsequent work, and 3) they just had no interest in acting after that one or two films. Jack Birkett/Orlando, for example, when in English-language films, has worked almost exclusively in Jarman films (followed by odd Shakespearian bit-parts from other independent filmmakers), implying that he was a friend of Jarman's or some other acquaintance that Jarman gave film work to for one reason or another (such as liking the way Birkett looked and casting him for that reason). Now, Birkett is an exceptional example here, having an incredibly distinct look, he's not one easy to cast in typical parts, and even as a "character actor" is regarded as so unusual-looking as to be unusable in the majority of films that get released.

Jarman's films, especially his earliest ones, were cast largely by unknowns, the "acting" was minimal (and in some, like Jubilee, the script was even minimal), and this doesn't offer a whole lot to other directors seeking actors for future projects -- and that's assuming that the actors want to do any "real acting" after an arty Jarman film. Thus, the actor falls out of the spotlight and presumably has a reasonably "normal" life.