unincorporate

Etymology

un- + incorporate

verb

1. To undo or remove the incorporation of.
   And if you are already incorporated, you may want to investigate the possibility of unincorporating, or at least electing subchapter S tax status for your business operations. 1987, Paul N. Strassels, The 1986 Tax Reform Act: Making It Work for You
   Unincorporating doesn't trigger a pension break in this situation: A doctor liquidated his corporation and terminated its pension coverage, taking lump-sum payout. But he continued practicing as a sole proprietor at the same address ... 1992, The Kiplinger Tax Letter
2. To not incorporate.
   There are consistent semantic differences between incorporating and unincorporating structures, … 1996, Maura Velázquez-Castillo, The Grammar of Possession, page 104

adj

1. (chiefly law, sometimes postpositive) Not incorporated.
   bodies corporate or unincorporate