An interesting case in which there seem to be at least 3 possibilities;
- Revenge by the Panthers (or, more accurately, their Omaha associates - since they had actually disbanded the Omaha branch before all of the events of 1970 due to inactivity).
- A fate unrelated to the events of 1970.
- Action by one or more of the LE agencies involved in the events of 1970.
I do not pretend to know which of these is most likely, but felt it appropriate to post this reply as noone has raised 3. on this thread. I would rarely consider LE action to be a reason for someone to go missing (except in the rare case of witness protection, which seems very unlikely in the case of a 14 year old left exposed for 2 years). However, in this case the level of venality, criminality and corruption by multiple LE agencies requires it to be considered. The background to this case is centred on the Omaha bombing of August 1970. Marialice Clark was used as an informant to justify action based on supposed knowledge of arms and explosives at the Committee House (although even the FBI did not believe this was true). In August 1970 someone lured police to an abandoned building and an explosion killed one officer and injured another. This led to the conspiracy amongst multiple agencies to convict Rice and Poindexter (the 2 leaders of the Committee). I do not know whether they were guilty. I do know that the LE agencies manufactured a case and had good reason for removing any embarrassing risks to their conspiracy. Was Marialice one of those? It is one possibility.
Anyone who wants to look further will find a concise summary on Wikipedia (under Rice-Poindexter case, as cited in #1 above), but there are many msm articles and books which cover the same material at more length.