Do I check the Complete Disposition or Disposition Was Not a Sale block if the K-1 is a final K-1? All properties in the real estate partnership were sold?

Yes, it would be considered a complete disposition if:

• it is a final k-1 and
• if all the investments were sold and
• your investment was liquidated,

You should have received information provided to you with the k-1 as to the cash/property distributions received due to liquidation of your interest  to show on your return and how to do the calculations of it.