"The room disappears, after one has left it."
Translation:Der Raum ist verschwunden, nachdem man ihn verlassen hat.
The standard parsing of this sentence is as the Perfekt of the verb "verschwinden": Das Zimmer verschwindet (Präsens), Das Zimmer verschwand (Präteritum), Das Zimmer ist verschwunden (Perfekt). Note that in German grammar the Perfekt counts as a past tense.
If you consider "verschwunden" as an adjective derived from the past participle, your alternate way of parsing does also make sense to me.
Thank you. If "ist verschwunden" translates as "disappeared" - past tense in English - then the Perfekt makes the most sense to me.
If it translates as "disappears," though - present tense in English - it sounds as though "verschwunden" is more like a predicate adjective in English - provided that I'm not inappropriately overlaying English grammar onto German.
EDIT No, it's not Zustandspassiv, but perfect in the active voice. It looks like a Zustandspassiv (and that fooled me in my original answer) but you can't change it into the active voice. See here: http://is.gd/pCp703
The sentence makes perfect sense in German. Think of Harry Potter's Room of Requirement.