If you have a multi member LLC it is taxed as a partnership by default. If you get rid of all the partners except one you now have a single member LLC so the partnership is effectively closed and a final partnership return must be filed. Then the single member LLC will be reported on a Sch C or an 1120/1120S if you incorporate. Seek local professional assistance if you do not know the state laws involved (since the LLC designation is a state issue not a federal one).
