It's pretty obvious that the devs didn't plan on anyone intentionally falling to make the archetype useable.
At the same time, the RAW interpretation is pretty clear-cut - lose the ability, and you no longer have the "natural ooze form".
The proper fix would be to just make that ability extraordinary, or split it into two (one that grants the ooze form and is EX, one that gives the polymorph and is SU).

Of course, you can just play a Kitsune, Skinwalker, or other race that gains some natural form of shapeshifting without limited duration. Use your natural form of shapeshifting, never worry about not having a humanoid shape. Enjoy your two natural weapons, having unique access to compression, and if you dip a second level, even some decent damage reduction.