I don't know from experience, but in the past I believe the rule was to place someone on admin leave and allow them at least one re-take. I did have the habit of not taking the exam by the deadline imposed by HPSP and was told that my stipend would be suspended until I provided a score, but it never actually was; I think I took it and supplied the score prior to everything being processed.
Having said that, I have heard that the rules have changed quite a bit and HPSP is pretty hardcore in adhering to the guidelines now. Given that you said you are appealing being dropped, it certainly sounds like it to me. Logic would suggest that they would place you on a LOA from the program and see what happens with a re-take, but beauracracies usually do not operate using logic.
The MODS website usually has a pretty active forum, so I would direct your question there, or contact Arthur Covey directly -- if he's still the, "go to" guy.
Good luck.