How about kabei?
Kabei is a verb that comes from the Esperanto name of Kazimierz Bein, Kabe. So it's not directly derived from any particular language unless you'd want to count the etymology of Kabe's non-Esperanto name.
Here's kabei defined, if anyone's curious:
kabei. Agi kiel Kabe, kiu, estante tre vigla E-isto, subite k tute ĉesis verki en E.
In English, translated by me:
To act like Kabe, who, having been a very active Esperantist, suddenly and completely stopped working (writing) in Esperanto.
Personally I have seen and used this word occasionally not just for leaving the Esperanto movement suddenly, but for being active and making a considerable effort for any type of movement/cause and then suddenly dropping it, or sometimes simply to describe being interested in something and participating in it for a time but then losing interest and "disappearing" from the scene.